I can't get Lincoln to play fetch no matter how many times I have tried. She has been trained to sit, down, leave-it, stay, come - all the basic commands, but I can't get her to fetch, not even once. She either chases after the ball/toy and takes it in a corner to play with on her own or she ignores it entirely. I've tried balls, various toys, treat-filled toys, and nothing has worked - Every dog owner I've spoken with has told me that they never trained their dog to fetch and their dog just did it naturally. She is a mutt, our best guess is a mix breed maltese/border terrier. Any thoughts or suggestions?