I will have to agree with chief again because when u clue zoanthus, there is a possibility of the polyps detaching, dieing, getting lost.... When u allow the natural process to take place u have a better chance of reproducing more healthier frags.
IMO, breaking off a piece of rock that the zoas is growing on is the best way. i have even successfully fragged baby polyps this way. also the zoas seem to grow quicker after being cut. placing freshly cut frags in med/high flow speeds up the healing and growing process. again, JMO
use a razorblade edge at the end of the zoos.... take the razor blade and slowly unpeel where it is sticking to the rock(get under it)..
then slowly peel it back a bit and cut down the center (where its peeled on the bottom)