If the rock can be moved, just place it in the sand the the zoos will grow out over the sand. Makes it real easy to tear or cut off at that point.
If you really want to break it up, a hammer and a chisel will do the trick. You can get a small chisel in between the polyps. Only thing I have had issues with on combo rocks like that is one color will sometimes overtake the other ...
Very nice rock!
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,