The culvert above was plugged wtih a mud dam.  Mud dams are conducive to using The Comstock Beaver Cages, which can be placed in front of the dam with a small trickle of water passing through the trap.  Even a small leak in the dam will attract a beaver.   The traps are set in single door mode, upside down, with the upper end of the cage resting against the dam.  It is the closed door, of course, that is again the dam.  The lower end of the trap with the opened door is placed towards the pond, resting just below the surface.  Road fabric is used to cover the entire cage, even past the closed door right up to the dam.  Loose muck is then packed on top of the cage to conceal all of the fabric.  The trap will lie at a slight angle, raised perhaps a couple of inches at the closed door, leaving an air space. 

This shows a set and cage buried into the dam, totally invisible to passers by. 

Not only are the traps invisible, but better yet, the catch is too.
Pulling the fabric back reveals a small beaver in the cage.