the goby and shrimp will burrow, most likely under a rock and you may get to see them popping in and out. The Gramma will move sand and make a den near the rock, bust doubtful it will dig a cave like the goby. They will get along just fine.They dig? Hmmm... RG are on my "possible" fish list but I really, really want a watchman goby/ shrimp pair. If the RG digs would they be incompatible? Tank is 54 gallons in display (and not ready for anything living yet).