We use Frontline Plus(fleas and ticks), but the dog still gets a few fleas, and we vacuum the house frequently(no fleas in the house). I get the authentic product deeply discounted from ebay which is good on the budget. When I bought Frontline directly from the vet we had the same problem, so it's not bad product from ebay. I briefly thought about going all natural with flea protection, but we would still have the tick problem. What we've had to do is combine Frontline Plus with monthly flea baths. I'd like to go all natural with the flea soap in the future.
I was browsing Etsy when I saw this really nice natural dog soap for fleas. I have many of the essential oils mentioned in the ingredients for the humans in our family, so I could make my own... or buy a bar. Time and energy are at a premium(scarce, so highly valuable) around here.
Here a recipe using similar ingredients over at About.com: Easy Dog Soap Recipes using bug rebelling essential oils such as citronella, citrus oils, tea tree oil, and lavender.
This sounds very drying to a dog's skin, but that is the reason it kills the fleas: flea bath with original Dawn(no bleach formula).
And here is a good comprehensive article full of recipes for repelling rid of fleas and mosquitoes using natural ingredients such as brewer's yeast, lemons, herbs, eucalyptus leaves, strong soap(dehydrates fleas), diatomaceous earth, etc.
It recommends using diatomaceous earth(dehydrates exoskeletons of insects) in areas of the garden where your pets tends to go most frequently. I actually do this with the cat. He likes to roll in one area of the gravel patio, so I sprinkle the diatomaceous earth in this area. I also put it in his cat bed.
If you use a drying soap, I think I'd follow this up with a herbal rinse containing some essential oils, or herbs steeped in water, and a few drops of glycerin and aloe vera.
I wouldn't recommend using essential oils on cats. I've read that some of them are very toxic to cats. Check with your vet before using herbal remedies on your pets.