Hate these guys, had to catch dozens last year and still find one from time to time, generally with a trophy wall of snail shells. A basic fish trap made out of a regular water bottle works alright. Load with shrimp, lean against a rock near their hangout so they can crawl in but not out. Only problem with this is you will catch lots of random stuff as well. Best method I found was also the most tedious, flash light and tongs at night. Red light works best and takes practice but works pretty well, just takes a while.