My Golden Retriever, Jack had breath so bad he could clear an entire room. It was *that* bad! Horrid, disgusting, nasty breath! I asked the vet about it, and the vet said "His teeth look clean and gorgeous".... we were clueless and willing to try anything.
I know I probably shouldn't have, but sometimes I'd slip him a Listerine Strip or Tic Tac if we were having people over or I was taking him in the car with me.
I switched to Wellness food and within a week, that was one of the first things I noticed. His breath was clean! No smell!! Amazing.
Curious- Does your dog perhaps partake in the evil doggie ritual of snacking in the kitty box? Nosing For Kitty Roca? Snackin' on Cat Turds? (sorry got carried away ....
Jack will still do it if someone leaves the laundry room door opened long enough for him to get in
omg that's the worst- so bad it seriously makes me gag!
I'm sorry I can't help you - I can sympathize a lot though!
Good Luck in figuring it out and let us know what you come up with. I considered those greenie treats! I never got them because his breath cleared up just fine for some reason when I changed foods.