I've used "bug off" garlic in Boo's food. it's basically just garlic powder that is marketed for dogs. Same stuff I think, though.
My issue with it was that Boo really didn't like the flavor of her food when I would add the recommended daily dose to her food. It *did* help with the ticks though. Now, when we go in the woods in the midsummer, I mix the garlic powder with water and rub it on her lower legs. She smells a bit like an Italian dinner, but it seems to help repel the ticks.