I went to "Toys-R-Us" and bought a couple of their hop balls: 15" ish plastic inflatable ball with a handle kids sit on and hop around.
I tied them inside the covered loafing area about 2' off the ground. Works great. The shed covers a walkway from the loafing shed where I keep the salt, and the trough where they eat. Fun to watch them go out of their way to whack a ball as they go by.