I usually mix up some of the stick epoxy (whatever brand you go with), then take part of it and secure it to the piece of coral, and take the other piece of epoxy and really press/ wedge it into the live rock where you want to place the coral, leaving a bit of hill of epoxy, then before the epoxy sets push the two epoxies together with a slight twisting motion. This way you don't have to put extreme pressure on the coral frag trying to secure it to a rock.