Live rock/Coral Glue?

[jostafew]

Best stuff to use (may be permanent depending on how you apply) is the 2-part epoxy putty you get at the LFS. Mash it together like playdough then apply between the rocks and spread out. It's a mechanical bond (not sticky like glue) so if you want a permanent connection be sure to cast it around some good features in the rock. I also use it to position stony corals in the same way. The epoxy may be used underwater, but i'd suggest doing the bulk of the work outside the tank as the putty tends to cloud the water as you work with it. Non-toxic, but doesn't bad until it clears.

For softies I like to use CA glue from the modeling world. Small puddle of CA on the rock, then just put the coral's base into the CA puddle, give it 10 seconds or so to cure up (moisture kicks it off) and then place the new assembly into the aquarium, preferably in a low-current area until the glue sets and/or the coral begins to attach itself to the rock.