My kids play the silliest game with her. She has a toy stuffed Mallard duck. My son has a toy gun. They go out in the yard, my son shoulders the gun and shouts, "BANG!" and my daughter throws the "duck" as far as she can. The dog happily dashes after the "duck" and brings it back to my son, who gives her a treat. It's side-splitting to watch, and they all love it.
She has begun to retrieve items strictly on hand signals. We were walking along a creek just last weekend, and she would retrieve junk out of the creek if I pointed her to it, and bring it back to us. (Tennis balls and milk jugs, I didn't point out any spare tires or tin cans. She did once, however, bring me a bowling ball in my living room.) She didn't care a rap about the two real live Mallard ducks that were coasting in an eddy on the other side of the creek, but I didn't point her at 'em for fear that she would go and get them . . . if birds hit the glass in our back yard, she goes and gets them and brings them to me. One wood thrush even SURVIVED this treatment.