Here ya go...

"A tick repellent can be made for both animals and humans using tea tree oil as an active ingredient. Start with a 2:1 mixture of your favorite base oil, such as almond or jojoaba, and water. Combine this into a spray bottle with 2 oz. of tea tree oil. For best results, use a glass bottle. Oils such as tea tree oil react with plastic and may cause dangerous chemicals to leech into your repellent. Before each use, shake the bottle vigorously to thoroughly mix the oils. When applying to pets, rub the repellent under their fur so that it reaches their skin".