8 months is way to young. An i would'nt judge a pup or muture dog by the way he acts on the chain or how hard he bits an shakes the hide. I went to a guys house one time an he had some pants on a fence for the dog to fight an tug on. He kept telling me look at the way she's ripping an bitting them pants an saying how bad she was. We put that bitch on a hog an she got her ass whooped an was a straight cur. So i would'nt rush an risk messing up your pup on how bad he or she act on the chain or kennel.