My method here was to first grab ppe, like glasses.
Then get big bone cutters, and clip the rock off from the main rock. I always did it in a bucket to contain any spray or pieces that shot off from the main chunk. Hammer and chisel works well too, but is a little less precise.
Did I mention the ppe? Glasses and maybe a facemask. I always looked away when making the real cut.
I used to do an at my house zoa fragging workshop for anyone who wanted to come by, and felt pretty comfortable with my method. If you don't feel like you are making progress with the rock, you probably aren't using big enough bone cutters. Force x Radius = Torque. Get a bigger radius, meaning bigger bone cutters.
Wash your hands after, and wash the corals off with tank water that gets discarded.
Zoas likely don't have palytoxin, but better safe than sorry.