First I heard of JB weld. Isn't that a two part mix thing? I'd be scared of it, but I guess both parts may be the same thing in super glues. I know super glue is widely recommended and used. Thing is, you really gotta pat kinda dry (out of the tank of course) the coral at the spot you're gonna apply the glue. Wait a few seconds I believe, then stick it in the water and hold it on the spot until it takes.
"Life may not be the party we hoped for but while we are here we might as well dance!"