You need to secure your FOB before you plan to attack, if you steal staff or materials people usually go out for revenge and take their staff back, you need to make sure they cant get in and take back their staff. (Note: This guide is for people who understand security settings up to a point where they know what most things do) Set your preparedness to max, this will make sure that your base automatically will have a-lot of things set up and you wont have to constantly check and increase the number of stuff manually.

This is the most important step as you need to decide your staff's neutralization methods, without touching it your staff will always be mid-range lethal, depending on the platform different ranges and lethal vs non lethal matters, you don't want to have long range staff in close quarters battles with the invaders, all of the platforms mirror your mother base platforms in design besides the addition of security devices, so get familiar with each platform and see which range suits each platform best. Note that mines change as well when you have the method equipped, Lethal has directional mines which can be picked up from its back but non lethal provides area denial sleep mines which will trigger if you walk near or over it but will not trigger if you prone walk up to or over it. Sleep mines are most of the time an instant KO whereas D-Mines are usually not a Kill. UAVS are also changed depending on the setting, Lethal UAVS at low levels will be equipped with a simple 5.56 caliber Machine gun with rapid fire capabilities and Non Lethal at low levels will be equipped with a smoke grenade launcher that takes some time to reload whereas in higher levels the Lethal UAV can have (this is word for word) "Battery Vaporization" which is a fancy word for if you are in the vicinity of a lethal UAV your battery powered items (NVG and such) will lose charge over time and the Non Lethal UAV is equipped with a sleep grenade launcher that has a faster fire rate than the Smoke grenades. Not just UAVS are changed, All emplacements that you extract in free roam or missions of any kind (FOB or Story Missions) are used in your FOB, but they can be stolen and destroyed as well if the intruder chooses. If you chose Lethal for your settings, they will work like they normally do in free roam and missions, they are made to kill and they do it well, mortars fire mortar shells (they have the same damage and AOE as standard grenades(plus the same icon)) and AA/gun emplacements fire very lethal bullets, whereas Non Lethal emplacements is designed to knock out the intruder in combat, Mortars fire Sleep grenades (the equivalent, but technically its a mortar shell) that KO the intruder if they stay in the sleepsmoke/smoke for too long, all AA/Gun Emplacements fire less lethal Rubber bullets that can knock out the intruder if they get hit too much. Non lethal mortars are in my opinion better at their job than lethal mortars as Sleep grenades last roughly 10 seconds before it goes away whereas lethal mortars just do one instance of damage and you don't have to wait to go back to the position the strike was in.

Deciding staff rank will be a big factor as E ranked staff are less aware and are worse guards than S ranked staff respectively, but are more expendable. My recommended ideal is if you can acquire that ranked staff easily and reliably then choose that rank. Higher ranking staff (S and above) will usually call out strange noises and if they don't give a SITREP then CP will tell all units to be on alert and all units will begin patrolling and tightening security and such. This is very important as people can Ghost bases with ease if you have low-level staff.
TL;DR
E-A Bad
A+ Below Average
A++ Average
S Above Average
S+ Great
S++ Best

What is Staff equipment? Staff equipment is the items you see in your development menu that has a green tint to their name, if you develop higher ranking staff equipment then your FOB staff have better stuff (pretty simple concept am i right).
Remember, all staff wont use the same stuff, non lethal will only equip the developed non lethal weapons (Stun and ZZZ weapons (ZZZ means tranq/sleep)), and lethal will only equip damaging weapons developed (DMG).

Staff Equipment Needed: Battle Dress V. Sneaking Suit (the ones in green).
Lethal guards will equip the Battle Dress (if developed).
Non lethal guards will equip the Sneaking Suit (if developed).
There is huge differences between the two, such as Sneaking suits being equipped with gas masks that prevent smoke and sleeping gas from effecting staff, whereas if you get Battle dress to lvl 5+, it will be equipped with a helmet that protects it from all tranqs to the head, but not the face (the eyes) besides AP (not quite sure on that though, it might not go through helmets).
Sleep darts will not at all go to the the body when the battle dress is equipped making stealth harder when your guards are set to lethal, whereas Nonlethal does not protect them whatsoever from tranqs but they are unique in the fact that they are protected from coughing when smoke is tossed or getting knocked out when a sleep grenade is tossed, if you develop the Night vision goggles from the Security devices development section it will equip all guards with it regardless of lethal or non lethal but they need to have the either the Battle Dress lvl 5+ and Or the Sneaking Suit lvl 4+ before they will equip NVG's. NVG's are important because the guards can detect you from further, and they can see through smoke if equipped.
Another key factor when deciding between non lethal and lethal is that when you equip the NVGs versus non-lethal guards they wont show up as the sneaking suit masks their heat signature in TPP lore so trying to find non-lethal guards when you have the NVGs equipped will be very very hard. Keep in mind lvl 9+ both Battle Dress and Sneaking Suits are equipped with stealth camo that activates when an intruder is detected)

So, someone noticed your base and decided to invade/ steal your stuff, if CP sends an alert then you or your supporters will get an emergency mission notification and they can deploy to defend, (note that if someone invades you because you had security challenge on, then only you will get the notification and not your supporters.) within the time you press it you can equip your stuff to defend, i suggest a rocket launcher and a grenade launcher for primary and the Tornado-6 and the Uragan Air-S for secondary as well too.
Once you are in, you will at one point see the enemys FOM (Field of movement), this can either be a FOM decoy which you can develop or their actual movement (note they are always in the center of it). If you damage or hit them with anything (besides smoke) at any point in time, it will raise a combat alarm and your guards will go into combat with the enemy and depending on the range will act accordingly.
If the enemy takes out many of the guards, a request from a surviving guard for backup to CP will be called, at which point members of your combat unit (not security team) will show up to assist. (Note: if the enemy deploys a FOB unit to disable reinforcements then CP will say something like: We have nothing to spare. (most of the time people will deploy a unit to stop reinforcements)).
If the enemy gets away a guard will say something like: "Lost visual, heading to last known position". If they lose them they will start a search for roughly 1-2 minutes but after that they will be on alert status for 4+ minutes (on anything but combat alert invaders can go into the core). If you kill the enemy rather than stunning or KOing and fultoning or whaling then your security unit members will get the medal of honor if that happens (plus its safer to kill the intruder rather than fultoning if they have been knocked out)

The second step to a good security is choosing where to place your mines and cameras. Requirements:


(Note that my FOB is on the North Atlantic Ocean so placement areas might be a tad different.)
Best placement for Anti-Stealth

Notice how the mine just touches the ladder so that they cant dive down or ladder down, they have to use the railing which further increases their chances of being detected, and if you place a camera like such:
Then they will have to use another way furthering their time spent. I place one camera right before the last platform as if they will try and rush they will be cut off, and if they stealth they have a greater risk of being detected. Another great placement option is near the material containers as its where most people go, be sure to save them for the red containers as the red ones contain more. (On non lethal regular cameras are used for both player placement and auto placement).

Lets say someone super high level invades you, they have max level wormholes, energy walls for days and it feels like you cant kill em or knock them out, you feel helpless until..... BUM BADA BUMMM: Introducing the brand new thot-b-gone weapon, the Fulton launcher, it goes through energy walls, it goes through armor, it goes through the C.Box, it doesnt activate their wormholes, better yet, it can snag pesky cheaters as well, and its doesnt use any medicinal plants to deploy with it, there is only one downside to this beauty of a weapon, you need to hit them dead on, no AOE crap, just hit their hitbox with the shell and bam you win. Why hasnt anyone used this; you may ask, because people like following trends made by people back in 2015-2016. It's so good because it's an underdog weapon. Keep in mind its terrible everywhere else but FOB Defense.

I have gotten the most success out of this setup with minimal losses
Command Platform: A++ Long Range Lethal
Combat Platform: A++ Long Range Lethal
R&D Platform: A++ Close Range Non-Lethal
Base Development Platform: A++ Long Range Lethal
Support Platform: A++ Close Range Non-Lethal
Intel Platform: A++ Close Range Non-Lethal
Medical Platform: A++ Long Range Non-Lethal

3/28 Updated information due to human error about the battle dress and sneaking suit minimum levels for NVG (Previous "You need to have a think lvl 4+ on the battle dress to have NVG") New: "You must have Battle Dress lvl 5+ or Sneaking Suit lvl 4+
3/29 Added in Step 4.5: Keep in mind lvl 9+ Battle Dress and Sneaking Suits are equipped with stealth camo. Added in Step 2: UAVS are also changed depending on the setting, Lethal UAVS at low levels will be equipped with a simple 5.56 caliber Machine gun with rapid fire capabilities and Non Lethal at low levels will be equipped with a smoke grenade launcher that takes some time to reload whereas in higher levels the Lethal UAV can have (this is word for word) "Battery Vaporization" which is a fancy word for if you are in the vicinity of a lethal UAV your battery powered items (NVG and such) will lose charge over time and the Non Lethal UAV is equipped with a sleep grenade launcher that has a faster fire rate than the Smoke grenades.
3/30 Added in Step 2: Not just UAVS are changed, All emplacements that you extract in free roam or missions of any kind (FOB or Story Missions) are used in your FOB, but they can be stolen and destroyed as well if the intruder chooses. If you chose Lethal for your settings, they will work like they normally do in free roam and missions, they are made to kill and they do it well, mortars fire mortar shells (they have the same damage and AOE as standard grenades(plus the same icon)) and AA/gun emplacements fire very lethal bullets, whereas Non Lethal emplacements is designed to knock out the intruder in combat, Mortars fire Sleep grenades (the equivalent, but technically its a mortar shell) that KO the intruder if they stay in the sleepsmoke/smoke for too long, all AA/Gun Emplacements fire less lethal Rubber bullets that can knock out the intruder if they get hit too much. Non lethal mortars are in my opinion better at their job than lethal mortars as Sleep grenades last roughly 10 seconds before it goes away whereas lethal mortars just do one instance of damage and you don't have to wait to go back to the position the strike was in.
5/29 Making custom placement guide
3/30/2022 Updated relevant information to make a more coherent guide