I use a slingshot for cheap n' quiet bird, tree rat, and stray cat control. Ammo of choice is the dollar store sack o' marbles. Kills feathers, knocks fur piss silly.
The damn squirels have it in for me. I was sitting on the patio reading when a week old rock-hard biscuit comes flying out of the maple tree and *CLANGS!* off the folding chair next to me. I look up, and there's this squirrel sitting on a high branch with a "shucks, missed!" look on his face. Wrist rocket was purchased soon after, and accompanied me outside on warm, sunny days.
I've also had green tomatoes (stolen off my own dang tomato plant! The nerve of these guys!) dog food, and assorted nut hulls chucked at me. I think the Squirrel Resistance Front is gearing up for something major, but the NSA, CIA, and FBI have ignored my concerns, in spite of growing evidence of an impending large-scale squirrel assault. . .