This is just the way he is. When we had him fixed when he was a pup the vet said that the room had this gagging stench in it from him. We have tried a few different foods over the years, no change. Some days he is not all that bad, but others.....
Our baby girl Dinga will do this real pretty sit right in front of you, all proper like with just the tip of her tail wagging. Just while your thinking "What a good girl", she squeeks one or two out. It's pretty funny and we thank god she doesn't have those smelly puppy farts anymore.