For a 100-pound dog (adjust proportionately to other weights)
1 heaping tablespoon brewer's yeast
1 level teaspoon garlic powder (or 3 or 4 garlic capsules)
These ingredients are inexpensive when bought in bulk, and besides being an effective flea and tick repellent, they provide vitamins and nutrients and promote a glossy coat. This combination emits an odor through the pet's skin that pests find very offensive. The ingredients also make the animal's blood taste bad. which discourages ear mites, ticks and other biting pests.