I'm a firm believer that those chemicals made to keep fleas and ticks off are just adding to a more serious medical problem.
Here is a site that may help you. I use the all natural products and mine have never had a flea or tick, and we go into the woods for camping.
Chinaroad Lowchens of Australia - Ticks, fleas, bees, flies, snakes and other gremlins! And how to deal with them!