Diotomaceous Earth (DTE) is a natural way to kill fleas, it is a powder that can be rubbed on the dog or in its bedding. The granules don't hurt the animal, but slice the fleas to bits when they walk through it. (It works in the garden also) It unfortunately does nothing for the eggs, but it does kill fleas.
Also, Neem Oil is very effective at ridding a pet of fleas. It is natural, but not fully non-toxic, you don't want your animals to eat it ever - but it can be used topically to kill fleas/eggs and mites that cause mange. you can buy products with it already properly diluted - it does stink to high heaven though is the only downside.
Cedar is also a deterrent to fleas, it doesn't kill them but they don't like it so they avoid it.