I use tea tree essential (organic) oil.
I don't know about ticks, but it sure holds off mosquitos and fleas (I'm a magnet for mosquitos and fleas in summertime - fleas bite me all the time when it's warm and damp weather - I don't have animals at home, but they bite when I'm walking in town, especially when there's a lot of people around like on city festivals or so).
It also helps for itching - just apply it and the itching goes away, so no infection because of the scratching )