There are a few different ways to propagate zoanthids.
1. Peel them off of a rock with a razor blade and super glue to some rubble.
2. Actually break apart the rock that the zoos are attached to with a pair of heavy duty cutters or a hammer and chisel.
3. Lay rubble or shells against the rock the zoos are attached to and patiently wait for them to grow onto the rubble or shells. This method can take a long time though.
What ever you decide to do be sure to WEAR GLOVES.
Many species of zoanthids are very toxic.
Try this link for more information:
http://www.fishtanksandponds.com/marine/Zoanthids.htm