Have your vet check his thyroid, sometimes when the thyroid is off it can affect temperament. This kind of dog requires a lot of management, it is not easy to live with and my hat is off to you for giving it a go. I had a young JRT that was human aggressive, he would give no warning, just lunge and grab and saw children as prey and would scream when ever he saw a small child. The breeder told me to put the dog down, so I did, it was a tough decision but once he was gone I realized how stressful he made life for not just me but my 2 other dogs. He offered me another dog but I decided to get another breed, that was when I got Huck. Some dogs are just wired tight and no amount of training is going to change that and no amount of training is going to make them trust worthy either. Good luck to you.