You can use a wood chisel to get the colony off, taking a bit of the rock with it. That way they don't come back. (Unless you miss some.)
You could also cover them with kalk paste, although for obvious reasons I'd do a small section at a time.
I have bad news for you, though. My very first coral over a dozen years ago was some pink clove polyps that arrived on some rock. Eventually I used the chisel technique to remove it "all" and sold it for frags. Fast-forward several years later and when I moved cross country there was a snowstorm and a delay, and my live rock FROZE. Guess what survived and started growing as soon as the "dead" rock was in a nice warm tank again?
Yep, I have pink cloves again.