My 5 mo. old boy is still in crate training, though he is really getting the hang of doing his business outside. He still sleeps in the crate, and he is in it when I go out. He gets plenty of outside exercise, physical and mental. I know how important it is to keep them mentally stimulated, so can anyone recommend specific tool, games, gadgets, etc. I can put in his crate to give him something to do? thx !