He's smart not to want rawhide! Bad for his digestion. Ham or anything smoked is also not good.
If you are giving the marrow bones from the butcher, the marrow is very rich and does cause some diahrrea...but getting a knucklebone with cartilage is usually much easier on the gut, aids in teeth cleansing and the cartilage is healthy nutrition. I would not give a whole turkey neck all at once, there is alot of bone in one, I'd cut it in 1/2.