Aggressive 17 week old puppy

Hello everyone! I'm new and I would like to know if anyone has any tips for me.
I adopted a Jack Russell Terrier Mix with a huge attitude. I work at a vets office and he came in to us barely alive. He tested positive for Parvo. The family who owned him was one of those families that doesn't have any money for treatments and certainly not for vaccines. So he had never gotten any vaccines and had never seen a vet before that day. So we agreed to do the bare minimum for this puppy because of their funds. We did 1day worth of treatments and then he started to perk up. It was looking good and we thought the bare minimum may actually work for him. Then he started to feel so good that he become an aggressive, attacking, :evil: puppy. He was Cujo in seconds from what I think was a lack of socializing. We were the only strangers he knew outside of the small family. We tried very hard to give him treatments but we were having an extremely difficult time. It got so bad we couldn't get him out of his carrier. So I did all treatments possible in his carrier with huge thick gloves on and tried to help him warm up to me. His owners came to pay some of the bill but once we said how much it was they suddenly only had 30.00. We eventually adopted the 17week old puppy and offered to treat him for free with the option to buy him back. The owners were called to give an update and they said we had the wrong number after calling that same number several times and speaking to them. It was really frustrating. So anyways, we got the puppy back to a healthy state but he was still very aggressive. I spent a ton of time with him gaining his trust and he slowly warmed up to me. We took baby steps and now he's a great active little puppy. BUT! The only way he knows how to react is to bite and not the play kind. He growls, shows his teeth and lunges when I reach down to fast and pick him up or if someone he doesn’t know tries to pick him up. He's gotten much better but now he's biting my other dogs over food. He gets fed alone but I want to know if I can get him to eat with my other dogs. I know this may sound horrible but I don't have time to take him to training classes but I can do a bit at home. What else can I do?:usa:

Wow ~ he's a "handful". It's a good thing he came into your hands !!

First things first right ? Has the Vet established that he is physically sound ? In other words, there's no physical reason for his aggression.

And you do know that Jacks are very territorial and food- dominant/aggressive period-the-end right ?

The first thing I suggest you do is try to run him "stupid". Once he's played out, it will be easier to teach him and he will be more receptive to learning.

The big thing ~ and this is something you have to wrap your head around ~ is "My house, my rules = nothing in life is free". Make him work for every single thing. Don't even glance at him unless he has earned it.

Yes, Jacks are smart...but you're smarter :D

Mummummum is right... tire him out! Jacks really are very bright - bright enough to learn fairly quickly how to get what they want. Consistency is the key with these little terrors!

They crave attention, good OR bad, and I found with mine that ignoring him when he acted badly worked better than anything else... when he'd bite, I got up and walked away, not even making eye contact for a few minutes. Lots of repetition, he got the idea that biting meant no attention and he'd give it up. Same with everything else - we make him sit/down/whatever before getting anything, and if he doesn't do it he doesn't get whatever it was and we try again later. Oh, you wanted that breakfast? Too bad, should have sat when we told you to, now you'll have to wait. Want on the bed? Same deal.

We LIVE 'nothing in life is free' here, and it works like a charm. Every person we meet swears our boy must be a mix, because there's no way any Jack Russell could possibly be this well behaved, LOL. But miss a walk, not have enough playtime, and you notice it! A combination of exercise - physical and mental - and making him work for everything keeps him a nice, well-behaved little puppy:) .

Your little guy is still young, work on him now and he'll be a wonderful and bright companion... and boy, I hope you have a sense of humour, because jacks are also some of the goofiest little clowns I've ever known! Good luck:) .