In general, in my mind, there are 2 rules for "fragging" leather corals:
1) cut decisively
- with a sharp blade/scissors
- without knawing it off bit by bit
(this will allow the coral to seal up the defect without "bleeding" too much, although you will definitely see a little cloud of white "blood" for a moment when you are doing this. A healthy leather will seal in 5-20 seconds in my experience.)
2) Attach the "frag" to a new rock. It seems that leathers are only happy (some say the same of some SPS) when they are truly holding onto a rock and have "grabbed on." This can be accomplished by either of 2 methods:
1. Rubber band gently to a rock. This is a delicate balance between;
a) rubber band being so tight that it slices the leather frag in two;
b) being so loose that it falls out...
2. Stick a toothpick (preferably plastic kind) through the leather (flesh!) and then use a rubber band to hold the toothpick, again not too much pressure, you could still split this guys in half!! usually facing the recently-cut edge towards the rock works a little better!!
P.S. I think all above comments also apply to Colt corals, not just Leather
