While cookies are definitely delicious... they can hardly be considered teeth-cleaning devices. Are crackers good for cleaning our teeth? Not really. In fact, they get stuck to our teeth, and the same goes for dogs. It's a common misconception that kibble/biscuits will scrape teeth when, actually, a premium soft food is much less likely to stick to the molars and promote plaque.

Have you tried trading Bob for bones? Like... what is something he finds irresistable? Fozzie used to be a brat about his bones being taken away, as a puppy. He even growled at me once, and he would always take off with it. I started bringing an over-cooked hotdog out to take his bone away. I would simply drop the hot dog a few feet away, take the bone when he went for it, and praise him. Now he leaves his bone when he knows I'm taking it away, albeit reluctantly. Teaching him that when a bone is taken away, something equally tasty is given to him really helped him to stop guarding.