We have a family of 5 who sprint around our garden every day, stealing entire seed feeders rather than just emptying them! Fat balls last about 5mins on the tree before they vanish!! They are extremely territorial, so must all be from the same family. I wonder if a fake squirrel would work, like the fake storks at the pond?
We also have a visiting rat this winter, quite fat and fluffy with a short tail. Oddly, he would only take pieces of bark from the play area and sneak them back to his hiding place! Totally ignored the peanuts in the tray!
When we had a dog in the past, we never saw rats or squirrels, as they could smell him I suppose. Perhaps if you own a dog, you could let him out every time he sees a squirrel so that they are chased away. They'll soon get the message.
Also, I wonder if that cat-scat remedy of "lions droppings" would work for squirrels. I've no idea, but worth a try for fun!