Just use a straight edge razor blade. Try to make a clean cut, don't use it like a saw. Place the newly cut frag in a low flow area for about a week, giving time for the cut flesh to heal. After a week super glue it to a rock outside of the tank, let it dry for about a minute. Place this in a low flow area for a couple of weeks allowing it to attach well. After that place it in a good spot for it in your tank. It's easier than you think.