Then I'd use superglue gel for the smaller frags. Larger ones may need the two part epoxy to hold them down and/or hide the frag plugs. Eventually it will encrust and you'll not even notice the putty. If you use this, or even crazy glue, watch your skimmer. They tend to go bezerk when you use glues in the system. It changes the suface tension of the water and you'll get more tiny bubbles than Don Ho ever dreamed about.
D