Permithrin, the only way to go into the woods. Apply let dry then wash it once with sportwash a day later, I get about 3 weeks out of a treatment when I wash'em regularly.
You may also try lavender oil, lemon oil, crysanthenim extract, etc... do some googling on the web and you will come up with many "natural remidies"
However they mostly all smell! effective but are quite strong, Good old permithrin, dampen your outerware with about 2 cans of the treatment, I use Repel permenone, let it dry overnight, your ready to go. For a MONTH!! I would not use it on my skin though.