I had a couple of wolf pups once, and couldn`t keep them in the yard. Raised the 4ft. chain link to about 6 ft. w/ barbed wire and put the top rail back on over that. The pups were still getting out. I then took an old elec. plug and wired the black wire to an insulated, (added) top wire , and the white I taped off. It didn`t use any electricity at all, until something touched it. The shortest haired one touched it w/ her nose, she never got close to the fence again. The long hared and prettiest one`s hair was so thick she would crawl thru it and it wouldn`t shock her. I ended up having to get rid of them. I didn`t leave the fence on at night , or when it rained , as I was afraid some one might get in to it. " DON`T RY THIS AT HOME, VERY DANGEROUS !"