Thanks for the article Geoff
Looks like I can't cut the polyp (which is what has attached) without real problems.

Either I have to find a way to A) coax it to move onto another rock, B) try to drill a chunks off the big rock that the bubble is attached to, or C) Trade in the whole thing where the large rock is worth more than the coral...
I wish I'd noticed the little beggar spreading, I could have put it on another, smaller rock
I'm most curious about plan A. Do bubbles move around like anemones? Mine never has.