The best way to keep them off your feeders is to make sure that you install a baffle on the pole and keep your feeders at least 10 feet away from anything that a squirrel can jump from. This includes other structures, feeders, trees and shrubs. Note in the photo, that the bird bath that a squirrel is in is places well away from the feeder.
There are two types of baffles - round, like a saucer, and cylindrical, like a tube (shown in the photo) - and both are effective. The idea is to mount the baffle below the feeder thereby prohibiting the squirrel from gripping and climbing over it.
photo © adrian binns