My tactics for squirrel hunting are walking up to it with my bow and taking a shot at it. I've found that squirrels let you get close enough to them, they're just so quick that they dodge the arrows. Squirrels will play with you too. It's like they know when you can shoot and you can't. I had a squirrel in a tree once in a place that wasn't a safe shot, so I moved to get a better shot. Then the squirrel moved into another way in which it wouldn't be safe to shoot. As far as air rifles I reckon you can chase em up a tree and wait for them to expose themselves.

Brandan