Garlic is fine in moderation for dogs. Onions, mushrooms, olives, baby food, cat food, any citrus, grapes, milk or dairy products, potatoes, raw eggs, yeast and chocolate should be avoided. A little garlic isn't going to hurt anything. As long as she isn't giving him a whole clove of fresh garlic or garlic everyday, it's fine. Just remember, garlic can lead to anemia in dogs, so just limit it to maybe once a week
Cinnamon is fine to give a dog, though, I have never heard of it being used to prevent fleas.
I wouldn't put any kind of yeast on a dog, period. Dogs can get yeast infections anywhere, and it could be harmful to put it on a female dog. Just FYi.
If you want a safe flea prevention, just stick with Frontline or Advantix. They work very well. You can also treat your yard if you want to avoid putting anything on your dogs.
Don't use flea collars. They only work where the collar is, therefore, making them useless.
We treat our yard for fleas, though, they are very scarce here. We don't put anything on our dogs and they haven't had a flea problem. We treated our yard back East also, and our dogs have never had a single flea.
