Like Franken said they always do end up moving, but on some occasions the fish will make an almost vertical burrow that they will stay in for months at times. For this to happen your fish must be extremely comfortable with its environment, and the sand levels half to be high(6" and up). Another good thing they look for is where the food is dropping. They will center themselves in the middle of the food if the fish is healthy. Another method that I've tried is to give the fish shells(penny-nickle size) they will use it for the burrow. They stack them up and form a more uniform burrow.