The only call I have had real success with is the "Squirrel Whistle" . I have found these work early in the season on Fox Squirrels. Basically they sound like a young squirrel in distress. Early in season the female fox squirrels come running.Sometimes even a gray will come in.Lots of times all of the squirrels will start barking and it will reveal their hideout, for a stalk. Seems like late Ocotber it almost stops working.