I might have a bad crab....soooo

[Oxymoron]

I have one just like this in my tank too. He is about 1" and lives in a spot that I can't get to without pulling all the rock.
So far he hasn't damaged anything and i have only seen him out of his "den" once in 6 months.
I did read on RC that some had sucess with burying a small cup in the substrate next to his den with a piece of food in it. Kinda like a mini pit trap that he won't be able to get out of.
I've yet to try it but it might be worth a shot.