I've been saying ffffffft to squirrels. Stick your upper teeth against your lower lip and go fffffft; they'll usually scamper. If you've ever heard a squirrel scolding another squirrel or crow or whatever, they say something similar, but screechier. Coming from an animal 200 times its size, I'm guessing that a squirrel doesn't care if the tone isn't just right.
I don't even give them a chance. If they're within attack range, they will be fffffffted. Take that, squirrel!
Squirrows, wow... That is one brilliantly bad pun! I think it's safe to say we have a winner for this thread!