I have heard of people using 2 liter bottles and baiting it with silversides. If you know where the hole is then you can bait the trap and put it in fron of the hole. If you know where the hole is then you can take out the rock and freshwater dip it. Good luck!
Those traps are just OK IMO, I have never caught anything in them except for detrius! Good luck with it all though...Maybe keep him....make a small tank for him...like BOB.