Deet is ineffective against ticks. Mostly.
Permethrin is the only sure deterrent. Soak your clothes in it and let it dry. Wear light colored clothes, long sleeved shirt and long pants tucked into socks.
The Permetrin should keep most of them off you. It really does work. Butttt - When you get back to your car check yourself over or better yet have a partner check you over. Have a magnifying glass in the car and tweezers. Use a lint roller on your clothes to pick up any stray hitch hikers. At home give all your clothes a ride in the dryer, set at high, for 20 minutes. The ticks that aren't roasted will be too dizzy to want to eat. Lastly, check yourself over in front of a mirror if possible. Again, this is better done with a partner, not to mention, more fun!!!!!
The rules are that - 1. ticks are down low where most of their food source is, inches off the ground. So, generally speaking, they don't fall out of trees. That said, they are genetically programed to climb up and will do so until they can go no farther. So, higher up is possible for the wayward tick. Just not normal. Once at the end of a branch/twig/leaf they wait for a meal to come along. 2. They won't attach right away. Again, once they are on you they will always climb up. No fast food for these suckers. Like us they are discriminating eaters and won't eat just any old place. Ideally they want warm and moist. But will settle if they are hungry enough.
The only way to avoid ticks is to stay out of their habitat, low scrubs, brush and high grass. Beyond that it's Permethrin and vigilance. For me, I'm out of the woods until first frost.
Hope this helps.