Scoop out most of the marrow (or all of it if his tummy is sensitive) before you give it to him. He'll still chew on it and amuse himself. Bully sticks and rawhides sit in the dog's digestive tracts and tend to cause mild food poisioning (hence the diarrhea and upset stomach).
You're much better off to use raw meat bones to satisfy his chewing needs. We use either marrow bones (Johann is fine alone with these) or rib bones (with supervision only- Johann chomps most of the bone part of rib bones). Make sure the marrow bone isn't small enough for him to swallow whole or choke on.
Johann has a deer antler that he's intermittently interested in. When I want him to chew on it...I smear a small amount of peanut butter on it and he suddenly loves it again.
