I dont think rib cages are going to work, Ribs have their little bit of marrow too. What you need are the heavier bones, unless you're carving plaques. Bury the bones in an ant hill or some such, anything to get ALL the meat. Museums use a special beetle but you don't want to mess with those, they can be dangerous. Once it's clean, get it good and dry or it may crack. I've heard a dozen different methods. Most of them work. Now, carve.