Bane of the Bird Feeder

I'll bet you didn't know that Dave, our Spring Lake Board President is an accomplished photographer. He shares this beautiful shot from his photo gallery, along with the following assessment: "The bane of the bird feeder! My arch nemesis!"
Ah, yes...what to do about the squirrels, who delight in frustrating those of us who feed the birds. Any solutions out there? Please post a comment if you've had success with keeping the squirrels at bay. What is your secret squirrel deterrent?