I throw in 10 or 12 cloves of garlic when I cook up their rice & pearled barley together, (4 cups of vegetable, chicken or beef broth, 1 cup rice & 1 cup of pearled barley) but I discard the cloves after cooking.
Here is a helpful site on using non-chemicals on the dogs to combat fleas, ticks and other insects.
Chinaroad Lowchens of Australia - Ticks, fleas, bees, flies, snakes and other gremlins! And how to deal with them!