Hi, sorry to hear about your problem. I am a dentist and have taken a couple of continuing ed courses on bad breath. Some people have such strong smelling breath that it is difficult to be in the same room with them. There is a device available called a halimeter that measures how bad the breath is!
Apparently there are a couple of non pathologic causes for this, however the culprit is always the same: Hydrogen sulfide compounds that reek of " rotten egg smell". There is an oxidizing agent you can purchase that neutralizes these compounds. It is called oxyfresh, I believe, and should be available at your vet's office.
I don't know how well it will work for your dog, but if all else fails, and there is no systemic cause for his problem, give it a try. I think you just pour it into his drinking water, but check with your vet for instructions.
Tom
