for montipora caps I get a 1 pound pies of base dry rock and carve it out a bit so the bottom of the monti is supported then use gel super glue I use quite a bit mostly on bottom side so the out side edge can encrust the base rock works well for me other wise I find a slit in a rock and place monti on it and let it encrust by it's self.

I am using epoxy for frags of branching corals like candy cane and the likes.

Bill