this is what i do. if i cannot get a skewer or something to put the glue on the rock with, then i apply an extra dab of glue on the frag, place it where i want it and wiggle it around, lift it, then press it down. this tends to smear some glue on the rock and also exposing the inside glue that ha snot touched the water for a tighter seal.This usually works for me.. First put some superglue on a skewer or ur finger and rub it on the spot where you plan to put your frag. Then try gluing the frag on that spot. It helps the glue stick together better in my experience.