When we rescued our puppy, Albus (yes, like Dumbledore), he was completely covered in fleas. I could actually see them jumping around on the ride home - it was horrible.
We used the dish detergent method to rid him of them, and then also for a while afterward to keep them away, but the dish detergent was so harsh that it was stripping his skin of its natural oils. He would get greasy and s-t-i-n-k-y within a couple of days of having a bath.
We started to try other methods: the flea collar, the liquid that you squeeze down the spine, but wouldn't you know, the fleas came back.
So we took him to the vet, who told us that everything we were doing was basically useless in Florida, and he needed some chewable pills. Those definitely worked. No fleas at all the entire time he took them, but.....
Then we started our essential oil journey, and began learning about natural options.
We started to see how essential oils were actually working for US as an insect repellent, and wondered it they'd work for Albus too.
He'd been without his flea chewables for months without a flea in sight, but then, we spotted some. Crawling around on his hiney, so I did some research and mixed up a dropper of oils that repel fleas, and guess what? 2 days later, we gave him a thorough inspection, and there wasn't a flea to be found!!
Here's what we used:
5 drops Rosemary
5 drops Peppermint
5 drops Eucalyptus Radiata
Topped with sweet almond oil (you could sub FCO) in a 1 oz dropper bottle.
We just squeezed a dropper full down his spine the way you would with those flea tubes at the pet store.
Albus is around 60lbs so we used about a dropper and a half. Use less for smaller dogs.