I agree with Cookie. Any breed can do flyball, although BC exell the most at it. It works best on a dog that loves tennis balls, and will allways bring it back to you.
I know GSDs can do it, as I remember seeing a few at crufts a few years back. Mind you, they didn't get into the finals xD
But, Its a fun thing to do with your dog. It'll increase your bond, and make them fitter ^^