No matter how you arrange your rock, he will spend most of his time under and/or behind it. It's just how they are. Now, you can arrange the rocks in such a way that he can feel secure while still being somewhat visible.
Also, make him work for the food! Come up with some sort of signal that indicates it is feeding time, and little by little, make him come out farther and farther to get his meal.
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef