I would agree with that but wish to add one thing more. Garlic and onions both contain an ingredient toxic to dogs, thiosulphate (although onions are more toxic than garlic) . Onion toxicity can cause haemolytic anaemia, a condition affecting the red blood cells. As Evie says large doses can be lethal also garlic should not be fed continuously without a break so if you are feeding garlic it is a good idea to feed for say four or five days then have a break for a couple of days just to be on the safe side .

I too put a garlic tablet in their food and they eat it along with everything else.
The other thing I do is make a spray up of tea tree oil and lavender diluted with water. When I used to have horses I used this as a fly deterrent and I use it on my dogs when grooming them. Little creepy crawlies and nasties hate it!!!
Mine are just 2 now and I have never seen a flea