I hate squirrels, and I'm not afraid (well...only slightly afraid) to say it. Why people keep defending them, I cannot imagine. As far as I'm concerned they are merely rats with cuter tails... They're just as prolific as rats--that's for sure! Black plague aside, I'm still not finding the antics of rats too interesting, either.
What I learned (from my earlier HP Question on how to keep them from digging up my tulip beds) is this: Cayenne pepper sprinkled around an outer ring may help deter them from climbing up into your Douglas Firs. Someone also suggested cinnamon as another spice they may avoid. I can't say this will positively work, since they had already cleaned out my tulips, but I suppose it's worth trying if you get a big 'ole jar of spice from the dollar store. Even the rat poison didn't help! Live trap? Phooey!
Oh, and by the way, squirrels also eat wood, as told to me by a friend who had to replace (at great expense) all the steps leading up to his lovely Victorian house porch because of these vermin. Dang!