I have to take his rock back to the store. I don't want it anyway because it is a man made rock, and doesn't blend in very well.

Is yours a BTA?
I just cleared off a rock for him, and set him on it, and put a plastic breeding trap over top so he can't wander away. Hopefully he will stick down on there. Do you guys find BTAs like certain surfaces? Smooth? Bumpy? Clean? Horizontal? Vertical? Tucked away in a corner?
If that doesn't work I will try digging a hole in the sand and placing him at the base of my live rock.