Displacements leaks

[Stertman]

Another question by me, I think I ask to much.. well.
Every single time i do a Displacement on a wall I get leaks. How the hell are you supposed to do? Im doing this cave, and I want to make it look more like a cave with some displacements on the walls, but nope, leaks every time.. Are there any secret secrets about this method?
Thanks

 

[JFry]

Displacements don't seal a level. You have to place world brushes (ideally textured with nodraw) under or around them to stop the leak.