Steve, I was thinking a little box propped up on a stick with a string tied to it. When it goes in after the bait, I pull the string, and wham!!, he's trapped. Well, ok, maybe that only works on birds!!
I'll drop a pop bottle trap in today and see what I catch, but I'm not pulling rock out (not that I think the rock could come out anyway).
I just find it strange that I've never noticed it before. There has never been any clicking, the liitle crabs I know about are still around, no lost hermits, my cleaner shrimp lives under the same rock. Just a fluke that I saw it crawling over a rock yesterday.