I agree I often use "BAAA!" or some noise that really scares them straight lol is sort of a deep squawking sound that I make from my chest and throut at the same time lol my friend thinks its the funniest sound ever, but it works like a charm! while we were walking her dogs and one of mine, everytime Dakota(her dog) kept turning around to get on Happys(my dog) nerves, I made that noise, he immedietly turned around and walked nicely lol also if you catch him chewing on something take one of his toys and trade, like "you give me that, and I will give you this" kinda thing. but if that does not work try the scary sound lol jacks can be rather hard headed, so start training him now.