I have used the "Mr. Squirrel" call before (The nickle sized one with the hole in center) in my back yard. I had a squirrel that started to leave my yard so I hit that call with four whistles first being the loudest, to quietest and that thing did a 180 across tree tops, down the tree, then on the ground came right to my feet at almost a run! I missed her at like 5 yards but it was FUN! She wasn't happy at all. However it seems that they learn that call fast and will go the other way.
Have a great day, HH