[Oh! Moving the rocks will NOT shake him out, so to speak! They would rather stay in a rock that is moving than come out. I know, 'cuz we killed one that way.
I was taking all the rock out of the tank to move it into a bigger tank. Never found the blenny. Come to find out, he stayed in the rock, which went into a tub of water - but it wasn't heated. Rough way to go - freeze to death!
And moving the rocks has probably scared him some. Get used to a new home, and have it moved on ya....]