I put my money in rock and sand. I have two engineers that are 10"+ and they stir the sand without anhillating my microfauna. I believe that the microfaunas role in this process is also a strong one, as well as what the gobies do. The microfauna helps to devour excess detritus, which helps keep the system in good balance. I have a feeling this is why people attain dead sand beds after a few years because there is nothing left alive as far as microfauna goes. It's speculation, but it's my best guess.