What To Do If Squirrels Are Raiding Your Bird Feeder

We have a bird feeder in our backyard and every time I fill it up, in addition to the cardinals, blue jays, finches and chickadees that stop by for a bite to eat, there are a couple of squirrels and chipmunks who stop by as well. They jump on the feeder and proceed to pig out. The entire feeder is usually emptied out within a day or two, and a couple of times the shepherd's hook the feeder is hanging on has been bent over from the weight of the squirrels!  What to do? Take a look at what this guy did-- and all it took was a little Vaseline!