stubby, I used to feed myself on gray squirrels back in my college days, and I used an Olt squirrel call, the kind with the little bellows that you tap against your hand or gunstock. While I was never able to bring squirrels on the run it worked very well to get them to move just a bit, especially their tail. I used it primarily to spot a squirrel that I had heard but not seen, or to spot one that had moved out of sight.
For that purpose, it was very effective.