DBD now has an override hook, which it calls whenever it thinks it should disarm something. Hooking into it and returning false will prevent it from doing so. The hook is:

DBD_DisarmCheck( victim, dmginfo, hitLeft, hitRight )

where:
>victim is the entity being disarmed.
>dmginfo is the damage that caused the disarm.
>hitLeft/Right are Boolean values representing whether the respective hand was hit.

Also potentially useful for development are the following convars:
>dbd_usehitpos - Whether DBD is doing 'expensive' checking, ergo making sure that the damage was done to the victim's hand.
>dbd_disarmforce - The force needed to disarm someone (two-handed weapons need twice the force).