I have used Epoxy and gel super glue, I even have tried both together, and so far I haven't found either to to stick to a coral or a rock in water. I use the RJ weld expoxy. And Have tried a variety of super glue gels. So far nothing that actually keeps the coral glue down. SPS are easiest to get to stay, but, soft corals, I nearly killed a beautiful zoa this past weekend, I was unable to get it glued down outside of water, let alone int he water. The I couldn't get the coral to stick to save my life.
I got one out of 5 SPS corals to stick, finally I gave up and just wedged them into crevices hoping they'll encrust... I haven't found a glueing method that works everytime.... It's the one thing that drives me nuts about corals... I've lost a couple corals because I thought I had them epoxied down, and the flow was able to blow them with the epoxy off the rock...