Fraging Zoanthids

I have a few zoanthid rocks that are so covered in zoanthids that they are stretching out about an inch to make room for more heads to grow. I think that zoanthids look better when they are close to the rock. So how do I get these zoo rocks under control? I have placed rocks on top of the zoos to get them to attach to those rock which they do but they also grow out from under the rocks. They grow under the rocks better then they grow onto the new rocks. I have placed new rocks on the edges to try to allow more growth but they don't attach them selfs to the new rock very well. What should I do? I like short zoanthids not long ones.

If you cut the zoos make sure you don't have any open wounds on your hands or touch your mouth or eyes.  They are very poisonous and you could become very sick. Super glue works great to attach zoos.