Yup, garlic in diet is great for repelling fleas and ticks, but I have found its effectiveness can differ in different animals. I use it with my dogs but they still get ticks fairly often and occasional fleas - which is to be expected since they roam our farm and woods all day! I'm still looking for the 100% natural miracle but for now I suggest trying garlic too!
Oh, another natural remedy is lemons! Slice up a lemon thinly (rind and all) and soak over night in just boiled water. This releases d-limone a natural pesticed. I then spray or wipe the juice over they coats to repel fleas and ticks. This also works much better on my short haired dog, but is hard to cover the fluffy long haired guys! Also you can use it as a rinse after bathing and let it dry on them for better coverage!