As much fun as it is making mine ladders, I don't think players should collide with mines. It's really annoying as a fade to blink into one and not only take damage, but you get stopped because the game seems to think it has a vertical height of at least 2 feet. It's also annoying on marines when you try to jump back away from a skulk and you touch the mine you were baiting him onto and you jump straight up instead which lets him get a bite or two in.
You could just make them like a func_illusionary, but when players touch the set area, the mine explodes.