Maybe the proximity mines could have an overall timer, so after a minute of two, they explode on their own, so people cant camp in a area protected by them.
Also, I've found a strategy in Facility, where you get the proximity mines, throw one down the maitence tunnel, one at the metal door, and one in the middle of the hall, then you hide at the bottom of the stairs. After the mines respawn, I go throw another one at the closed door by the stairs, and then camp there. Most people will die because of the mines, and if I ever need to leave the area, I have the room with the broken door. Because this is soo cheap, I was wondering if the mines could be moved to the top if the stairs in one of the tank rooms, so it won't be in a main area.