Ann, Have you heard of Critter Oil? Its really, really effective. The tick situation is crazy right now in Miami and I have only had one tick embedded in Louis, I did find others crawling (ewww) but, combed them right out.
You spritz the pooches with a dilution according to the instructions on the Critter Oil every time you take them out, then you need to get a flea comb, comb them EVERY time you take them out. Bathe them if you find ANY creepy crawlies and be prepared to bathe 3-4 times a week.
This is what I do and I am tick/flea free in Miami with no chemical pesticides whatsoever.
You can buy it here:
Critter Oil Flea Repellent
I am devout to this stuff! You can apply it to Wylie's collar too. Your dogs are on a healthy raw diet with great immune systems - parasites like fleas and ticks look for hosts with compromised immunity, so you are already ahead of the game. I wouldn't be against adding an immunity booster to their daily regimen as well, just to strengthen them that much more. I use Vetri-Science DMG.