Anyone have suggestions to keep squirrels out/ off the bird feeders?

My husband was surfing the net and found a "squirrel Flipper". It's a bird
feeder that will take the weight of birds, but not squirrels. When a
Squirrel sits on it.... his weight will cause it to turn and "FLIP" him off.

Though I think it would be very entertaining..... I don't want to be "mean"
to the squirrels. I just want them OFF of the bird feeders!
Dorothy

ps. We're trying the "slinky" solution right now..... but other solutions
are welcome!