I find that only large corals need epoxy. The gel works great for most stonies unless very big or oddly shaped.
A coupla tricks.
1. dry the spot on the rubble or rock off well
2. take your
dremel tool and make a hole/slot appropriately sized for the frag/coral you are gluing
3. put the glob of glue in the hole and let it sit for a couple of minutes
4. dry off the base of the coral and when you go to set it in the slot have a couple of q-tips handy to prevent the coral from sliming and ,etting the slime mix with your glue.........thats what messes a lot of people up i think
5. either hold it for a couple of minutes or put something next to it so it sits in place...leave it out for a couple of minutes.....it will be fine
6. while its sitting there, any parts of the base of the coral that have space showing fill up with more glue. The loc-tite glue in the plastic dispenser has a nice sharp tip to apply in tight places.....
doing all of the above makes the gel hold incredibly strong and eliminates the need for epoxy in the first place in many circumstances IMO