To me it sounds like the previous owners praised his bad behaviors when he would take something which would be confusing for anyone. I would begin to give treats when he does good things to retrain the idea.
Use a spray bottle for growls or bad behavior. Use it to startle but dont acknowledge the bad behavior. Act like you didnt see the water and dont let him see the water bottle.
The other main issue it sounds like is the socialization. I would suggest doing the basic obedience training in a Petsmart. You will have a trainer with you each time you go. You will be introducing your basenji to other dogs in your class in a controlled atmosphere. You will be in a busy store with people that will help him socialize and get used to the people.
Once you have learned the tricks or commands from class and your basenji performs them with you flawlessly. Have your roommate use the same commands and gestures until your b can do them with your roommate. Then add a friend that isnt around all the time and slowly teach the dog how to communicate and receive praise and treats for his actions.
I suspect that with this training, your basenji will soften that aggressive behavior and want the treats. The behavior may never go away completely, but you will always be around to keep an eye on him. If you have a dog walker, I would think that it is very important that your walker follows your guidlines for training to keep your dog safe when he is away from you.
Strangers who have been bitten by a dog have had the ability to put the dog to sleep and it is important that you do not permit him to find an opportunity to slip.
My rescue was food aggressive and fearful of everything. She had seperation anxiety, growled, and took 2 years to potty train. It is important to be consistant with your training. It is important to praise. My rescue settled down completely after 3years and I learned the triggers to avoid.
I would also suggest not having any pull or shake playing with your basenji which would mimick tugging or tearing prey.
When your basenji is relaxed, massage him. Touch his mouth, his ears, hold his feet. Teach him to understand that there is no off limit area. Have your roomate and dog walker do this as well once you feel he has begun learning from the training. Have your roommate help you bathe him, and so on and so forth.
As long as one of the 3 of you can handle him in basic training, around people and handeling him you should be more confident that you are protecting him as well as the many victims he could encounter in the future.
You know he is great and you want to take care of him. The best way to do that is by helping him learn to communicate with people, not out of fear.
Oh, and a soft muzzle is a great way to take him for walks with a dog walker and keep him from hurting anyone else. He can move his mouth, but wont be able to open it. I bought mine at Petsmart when Caesar was a puppy and eat his seat belt off when in the car going anywhere. Do not use it with punishment, but as a tool to let him know it is time to go for a walk!!
