I never put pesticides on my dogs. and never will, so I understand your concern about it.
Here are a few links for how to use essential oils for dogs as natural repellants. There are various methods people have used with much success. YMMV, but be sure to
research how to use the oils properly.
Essential Oils That Naturally Repel Fleas & Ticks | LIVESTRONG.COM Essential Oils That Naturally Repel Fleas & Ticks | DailyPuppy.com Essential oils for dogs | Essential Animals Tick Repellent for Dogs Goes Natural and Trouble-free with Essential Oils