Our kids have a Rottweiler that loves to chase a ball, Bring it back and then dare us to try to take it away from her. She can drop if convinced. Or I have a second ball that is more interesting, causing her to drop the other ball. She can hold two balls in her mouth so I have to wait for her to drop the first ball before I throw.

She also has a large (about 1 food diameter) ball that can't possibly fit in her mouth and I can kick that at which point she'll drop the little ball and try to get the big one in her mouth.