Keeping an actor in a circle

I need to keep an actor in a circular area but when i place the circle it acts like it is a square. I need to keep the actor in just the circular area like how a thumb stick never leaves the circle it is on.
Comments
Otherwise it is constraints or rules sets that work to keep that actor within the area you want. A magnitude from a certain spot will work if you then make rules that check this magnitude and use either a constraint or other rules that limit the actor from travelling further.
hope that helps
kipper
Search the title of the demo in the gamesalad creator to open the project
cheers