A good and natural way of freshening your dogs bad breath is to cut up some parsley and mix it in with your dogs food.
You can also add mint to the dogs food as well and both the parsley and the mint will help your dogs breath become fresh and get rid of the dogs bad breath.
Brushing your dogs teeth using some baking soda and water to make a paste can also help freshen your dogs breath.
You can also put some Apple Cider Vinegar into the dogs water once in awhile to help kill the bacteria that is causing the bad breath in the dogs mouth.
You should also get the dogs teeth and mouth professionally cleaned by a vet at least once per year which helps remove tarter and plaque from the dogs teeth so that the teeth and mouth of the dog smells better.