My brand of choice is any cyanoacrylate type super glue GEL that the DOLLAR store sells. usually the 3 pack of 2 gram tubes for a dollar. always use the gel. it holds and sets better. Also remember , as cyanoacrylate cures, it produces heat which can harm the live coral skin. so what i do is towel dry a chunk of rubble rock, put a big glob of gel on it, then take the hard coral frag and push it into the glob with one or two small twists, then hold and blow dry a moment till the frag stands by itself. then gently set in a bowl of tank water for 5 minutes to further cure, and keep the glue cool. then into a quiet spot in the tank to finish curing. do not work the glue or move the frag after that. it will just break loose. so a quick twist to cover the coral base with glue and hold still. simple as that.