US Patriot Defense Systems cost a lot of vital manpower that could go to more powerful elite infantry such as Deltas or the highly reliable Rifleman squad. They also take a while to construct - similar to the British, you want to snip in the bud before it gets setup - try to apply as much pressure if you believe he's attempting to construct this non-sense.

In addition, the Patriot System is only effective against aircraft and vehicles.
The hard counters to the US Patriot Missile System are as follows:

- Use Smoke Grenades and Anti-Tank Guns to destroy them. Patriot Missile Systems do not have attack ground meaning they are completely helpless against smoke but your anti-tank guns do. The Pak 40 and Raketenwerfer are extremely effective due to their sheer volume of fire - just be sure to keep them defended with infantry.

- Use Panzershrecks; they have a massive attack range as long as you have sight of the Patriot Missile Systems, they will shoot at them. Have a Kubelwagen or squad with 50 sight range spot for your panzershrecks. You can firmly shoot at him without ever getting shot back. Note that this only applies to the auto-attack range - if you right click and give them manual targeting orders, the squad will attempt to get closer. Just give them a halt order so they can shoot instead.

- Use artillery. Axis have some devastating indirect fire options. Ballistic Missile Bunkers and call-in artillery will make short work of the Patriot system as they can do absolutely nothing against it - this applies to all non-mortar type emplacements such as Machine Gun nests and British Bofor Gun emplacements.

- Flank and cut off his supply line. Engineers can only construct field defenses when the territory is friendly and connected to their base HQ. If you wanna stop his non-sense, then neutralize his territory cut-off points to disable his ability to build patriot systems - it'll force him to engage you but he's likely not to have an effective force.