If nothing else, I consider myself a pro matis catcher after nabbing 6 or so in my live rock from FL. I was relentless, and used every technique- coat hangers, nets, and hemostat. Taking out rock that it can be located in is best. Actually, placing rock with crevices in an accessible area of the tank for quick removal and capture is probably as good as a trap. Once you see it in a rock that can be removed, remove it at once and go about the business of extraction.
It took me about 10 months to get all the ones that came in my live rock. Some grew-up, cased some problems, but are now gone.
dpd