When helping an owner and dog the dog trainer asks questions to find out the problems even before meeting the dog. 1. How old is the dog? 2. What breed? 3. How long have you had the dog? Usually the question of where did you get the dog?, is not necessary as the dog owner has already told you. They rescued the dog and it was abused and on and on the story goes without really knowing the truth about it's past.
So you have had this dog since it was about 4 years old. It is now 10 years old and you want it trained not to bite you when you pick it up? Am I Correct? Is that what you are asking?
So you have raised this dog since 8 weeks old and it is now 2 years old and you blame its dog aggression on being a rescue. It may have dog re-activeness that was not tended to as a puppy or it has "dog hatter" in it's genes. Something the dog owner nor the trainer will ever know.
Dog Trainers get many different answers which are not close to what the reality of it is. The trainer must talk and evaluate the situation. The trainer must talk and evaluate the owner and the dog. Once all that is over the trainer only has that one dog in front of them with a vague history other than what the owner has told or the dog has shown.
With out going into training methods, this is where the trainer pulls all the tricks out of their bag and get to work. With just the dog in front of them. If training the owner they now have the owner and dog in front of them. The owner will always fill in the blanks even if it is their imagination. My dog does this because. Not true. Your dog does this because it can and is a self rewarding measure for the dog. Dogs like that. Dogs like when it works for them. And on and on the training goes until the dog no longer wants to attack dogs or humans.
Reactive Dogs can be Non-Reactive Dogs. That is the trainers goal.
Disclaimer: This is not all dogs but what many trainers see on a daily basis.