In the ocean yellow headed jawfish (others use different strageties) use a lg stone as a roof to the burrow, I'm not sure how they find it, as if you look at colonies they look like they are on sand and mud for the most part, but when we collect them, what we do is get close to the burrow opening, put a net over it, then dig about 5 inches around the hole. Within a few inches we find a stone, then we go to the part of the stone farthest away from the opening and go at the fish through the "back door". when you get close to the fish, it swims into the net covering the opening. I only tell you this so you can recreate this in your tank, take a flat piece of rock and burry it about an inch above the bottom of the tank (or planum bed, or what ever is at the bottom that the jaw can't get through) and then burry it with as much sand as you can. Give the jaw some rubble to support the burrow and you have a perfect habitat for him to dig in. Just remember, it may take him a while to be comfortable and build the burrow where you want it to, and jawfish frequently move their burrows. This is important because even jawfish will jump at night after they are establlished but are looking to move the burrow.
