I am having an IDENTICAL issue with Scout. In fact, I was going to post on the same subject. There are some excellent people with behavioral knowledge on the board. I hope they will come out and post for us!
I am almost afraid to talk about it, because I was one of those "my dog will never act like that" people...that's what I get
Scout has always been a bit of a mommas boy, but since he turned a year old he is doing the same as Penny. What used to be shyness is now agression. Toward strangers, little kids especially
I literally have to pick him up and walk the other way when I see little kids. The door is an issue, he goes CRAZY when there's knock at the door. I tried Cesar Milan's method of leashing him and having my kids go around and knock on the door-correcting him as soon as I see him start. I am at my wits end as well. He's the sweetest boy with us-he just doesn't want to share us with others.
Something especially strange I've noticed is that I can take him to crowd events and he does FINE! He doesn't bark at people...he trots along right beside us...it's weird! AND he did do classes as a puppy and has been socialized with other dogs. He's fine with big dogs, he's mean to my sisters baby yorkie/dachshaund mix. I can't figure it out.