The wildest squirrel feeder I’ve seen was composed of a, roughly, 2" by 2" put into the ground, sticking out about 4 feet high, with a hole drilled through its side at the top. Bolted to the post, via said hole, was another bit of wood, roughly the same dimensions, with screws sticking out of its ends. Attached to the screws were ears of dried corn.
The squirrels would climb the post and then jump onto the bit of wood that has the corn on its ends, which is free to rotate via the hole drilled into its center and the bolt that goes to the post, and the arm would start to spin around. Typically, the squirrels would get thrown off before they reached the corn, but some would figure out ways to get at it.
Another one, this one actually intended to feed the squirrels, that is really neat is the one found at the link to an article in “Birds & Blooms” bellow:
Most people enjoy the antics of backyard squirrels. That's why we think you'll have fun with this "squirrel under glass…www.birdsandblooms.com
That is a fantastic magazine, by the way. I can’t recommend it highly enough for kids or adults.