My vote is for sandsifting stars. I have had gobies in the past that have covered corals with sand. The starfish works just as well. I have had Linckia stars and red sea stars eaten by something in my tank (possilby one of the surgeon fish) but nothing has bothered my sandsifter.

I think that sand sifting snails are your best bet. All gobies have a tendency to jump and from what Ive read the only sure fire way to keep them IN the tank is glass. Anything with smaller openings than egg crate will start to diffuse the light too much.