I've been using essential oils to repel fleas/ticks for over a year with success. I never use any chemicals, only oils, and haven't even seen a flea on them yet. Ticks are a bit hard, but even the toxic tick poison doesn't always work. For ticks, I'd actually suggest Euclaptyus oil as it's been proven ticks hate it and I put it directly on a tick not too long ago and it died.
We make up a spray of water(filtered), or we use vinegar, ten drops of eucalyptus oil, and almond oil and apply that to dogs, humans, and yard daily.
Oh, we also drop a drop of straight oil on their collars each week and the smell usually lasts a week. I've also soaked their collars in the solution but I found it better to put a single drop of the oil on the collar, let it dry, then put it back on the dog. don't use essential oils on cats and don't let the cat around the dog until it's dried if you have one.
It works fabulous for us but then again holistics don't always work unless you live an entirely holistic lifestyle. Meaning using essential oils and toxins can make it not work because the toxins tax the body and fleas(not as much sure about ticks) will be more drawn to them because of this. It's worth a shot, though. It clearly works as we haven't had a flea (and less ticks)in 16 months! I've seen less ticks , but do occasionally find them If I forget to spray. We use Diatamacious Earth in the yard also and I, believe, it kills ticks.
GOOD LUCK!!