You want something that is too big for him to chew once and swallow. Also, something he can actually eat. Bones that are too hard damage the teeth. Wolves have big tough teeth, dogs don't. Depending on how big he is, you could start with chicken backs. That is, the spine, neck, and pelvis. Chickens are small creatures and are butchered usually at eight weeks so the bones are soft. As he gets bigger you could move to ox tail.
A round bone, being shaped like a ring, can get caught around the lower jaw, but you could cut it in half. Just remember, small enough for the dog, but too big to be swallowed whole.