A cleanup crew of hermit crabs, snails, serpent stars and shrimp will clean the rock pretty well. Strategically placed powerheads will prevent too much debris from settling.
Best option for keeping the rock of the sand bed: get a peice of egg crate (big box store, the stuff they put in light fixtures in office buildings). Cut a chunk out to the size you want. Use chunks of PVC to support the rock above the sand bed (we drilled holes in the PVC, and pushed them into the sand. One end sits on the bottom of the tank, then zip tied the egg crate to the PVC).