I've always used Advantix with good results. My mom's dog is on it, too, but he is still a tick magnet. I've read about people using Rose Geranium Oil as a repellant for their dogs, but have never tried it. I would make sure to ask my vet before going ahead with it's use.
Easy, Natural Tick Repellent That Really Works | Primally Inspired
I don't think there is a one shot approach that will work. In addition to the preventatives, being vigilant about combing them out when you get home will help. Ears and between the toes are especially attractive areas to ticks because of the increased blood flow. I wonder if wearing a little t-shirt on your walks would help prevent them from getting attached under the armpits.