German Shepherd Mix Aggression

Question
Breed: German Shepherd/Lab Mix
Age: 2 years 3 months
Sex: Neutered Male


I have a two year old German Shepherd/Lab mix who has become increasingly aggressive over the past 1 1/2 years. We got him when he was a puppy (about 2 months old) and he has had all of his shots since then. When we first got him, we made sure to socialize him right away. In the first week that we had him, he met around 7 other dogs and played well with all of them. When he was about 6 months old, we enrolled in a dog training class and he did very well with the other dogs in the class. When he was about 7 months old, he was neutered and we decided to adopt another dog for him to play with. When we adopted her, she was about 5 months old. She is a Husky/Chow mix. He played very rough with her at first, but plays much better with her now. After getting her, we started to notice that he acted differently around other dogs. The first time we noticed that he began not getting along with other dogs was about 1 year ago.

His aggressive behaviors include:
1) Barking and growling at strangers that pass by the house
When strangers come into the house, he initially barks/jumps/growls at them, but never tries to bite any of them and settles down quickly.
2) Barking, growling, and lunging at other dogs that pass by the house
3) He will try to bite any new dogs introduced to him.
4) He sometimes growls if our cats climb on him.
5) If we have dog treats out, he will sometimes growl and even bite other dogs around
6) He will sometimes growl if we give attention to an animal near him
7) When other animals come over, he sometimes goes to his food bowl and eats like he's protecting the food.

He has never bit anyone and does not exhibit food aggression towards people. We have never used physical punishment either.

I want to know why he is acting like this and what can I do to stop this. I realize that an animal behaviorist is the best solution, but I want to know if there is a cheaper way to fix his problem. I am willing to do whatever it takes to help him, so if my only option is an animal behaviorist, I'll suck it up and pay.

Thanks and have a lovely day.

Answer
Much of what you have done is good.  He is maturing and wanting to provide more leadership to the pack.  Additional obedience training may help.  So might more proper walks.  I am not into the 3 hour walk a day solves everything.  But getting him out on a good walk where you set the pace, choose where, no sniffing, stay on task and keep the leash loose, will show him you are in charge.  

That may or may not be enough to avoid thebehaviorist.