Actually, O. scyllarus can't burrow effectively in most aquarium sands. In the field they dig their burrows in a variety of substrates ranging from mud to muck and sand, but usually these have some cohesion. What O. scyllarus need to form a burrow is shell, gravel, and small to medium pieces of coral and coralline algae rubble. They line the inside of their burrow with such objects to stabilize it. I've seen burrow in shell beds that were entirely constructed out of poker chip sized pieces of shell and other burrows in fine sand lined with large forams and pieces of LR.
If you want your animal to "burrow" and not just dig a cave under a piece of LR, you need to provide lots of pieces of rubble, shell, etc.
Roy