I have a VERY large German Shepard who loves to run after and jump for rubber balls. We adopted him in June 2013 at 4 1/2 years old. We have noticed that sometimes the dog limps, but he doesn't seem to be in actual pain. I have given him Cocusmin and he got better, but he is limping again even though he is still taking the medicine. We can't get him to stay inside for any length of time to rest the leg… any ideas? Diane L.