You'll find the heavier the coral the harder it can be to use just superglue gel. What works very well is to use both marine epoxy puddy and superglue gel together.
Knead the epoxy, place a dab of glue on the epoxy ball and then insert the coral through both about a third the way. Add another dap of the glue on the other side of the epoxy ball and adhere to the rock in the tank where it will remain. The glue only takes a few seconds to set up and the corals weight will be a bit better supported than it would have been with just the glue.