I have always leaned against cutting them off unless you want a new one to grow back. Xenia and Colt corals I like to slowly tear off of the rock. This way there is no base for a new one to regrow. If you are wanting more corals just cut the bases about 1/4" from the rock and watch the nubs grow out quickly. This is just what I have experienced from them. Oh, and I also attach them by squishing them between two rocks. I typically put them in the fuge where they wouldn't be bothered.