yes it works underwater, but for holding rock together, that two part epoxy actually does work pretty good, you just have to use quite a bit of it.
When I glue sps frags to rubble, I pull the frag out of water dry the end off a bit put some superglue gel on it dip it in water (it forms a crust when the water hits it) repeat it a few times until there is a decent amount of super glue on it, then stick it to the rock and hold it there for a couple minutes until it cures a bit.
It is not special aquarium use, just regular old super glue gel.