Loctite super glue gel and JB weld waterproof epoxy from, Lowes or Hone Depot, like clay or silly putty. Make a small ball of epoxy will turn grey then put some super glue on bottom of frag or plug, push epoxy on to super glue then put more super glue on epoxy and push it on to rock where you want it. This should keep it in place, if you do a lot of them at the same time turn off your skimmer for a few hours or it will foam over. After some time the coral will either encrust over epoxy or it will get coralline algae and look just like the rock.