When busting up live rock in order to make small rubble pieces, be sure to use the proper tools and personal protective equipment (PPE). The hammer and chisel make for a great set of tools to hack away at some calcium carbonate rock, but the violent action can lead to flying shards of rock that could hit you in the face or some other exposed portion of skin. To prevent any injuries, at least to the sensitive eyes, make planned and methodical hits on the rock. Also be sure to wear safety glasses and maybe even gloves to keep from scraping your hands against the sharp edges. If you are more inclined to play with power tools, a rotary tool does wonders when cutting up rocks, though it may cause weird burning odors.