To be honest though, a proper diet for your dog would serve it best rather than feeding it garlic. Poor nutrition in your dog makes it a more appealing candidate for fleas, as fleas tend to go for unhealthy dogs.
There is also the possibility that your dog could have an alergic reation to garlic, so personally, I wouldn't want to take that risk with my pet.
[Edit] In regards to home remedies, you could try these although they don't always give you the best results:
- mix cut-up lemons with boiling water and let it sit overnight. Put it into a spray bottle and spray your dog around his ears and neck (be careful of his eyes). Spray along his back to his tail and under the legs and belly.
- mix some tea tree oil with almond oilm, add 10 drops of lavender oil and 5 drops of cedarwood oil. Put a few drops where you'd put around the neck and tail area two times a week. If your dog has collie blood don't use teatree oil as they can be sensitive to it (you can use the almond oil). A teatree oil and water spray is good for non collie dogs.
- Crumbling pennyroyal where he lays can work too. Try sprinkling it on your carpet and vacuum it up a few hours later. You can also plant it around your garden (or the dogs kennel if your dog has one) as fleas don't like it.
To locate more links search > dogs fleas home remedies
My dog doesn't get them much unless we visit friends whose dogs have fleas. I rely on the store bought powder and spray. They have carpet spray for fleas and I always use that on the carpet and furniture she sits on. A combo of these has been effective for me. Since she gets them rarely, she isn't exposed regularly to the chemicals.