I 2nd the crate training. It is great.

Find his focus. What will he do things for? Our dog just loves food, she adores smackos (we are sure she is addicted to them). To generally will do anything for a smacko.

Consistency. Keep to what ever rules you decide on. It seems tough, but they need to know their place in the pack to be secure and for you to keep some control over them.

DH grew up with Jack Russells, he said to be firm but kind with them and that he will bond strongly with you for rescuing him.

Best of luck. I also agree with L&B that if you can't do it, then let a proper rescue place take him.