First puppy, needing advice on training
So for Christmas we adopted a second dog, then a 5 month old sherpherd mix. He's now almost 11 months old. He gets along great with our 9 year old lab, and the lab likes having a brother. However I'm having problems with our shepherd specifically outside. He barks ferociously at every dog he sees, and starts pulling uncontrollably. I've read so many different points of views on this topic that I don't know how to approach it.
It was clear when we first adopted him that he was abused by his first owner. He was extremely malnourished, had a belly of parasites, and anytime I would raise my voice, he would instantly pee. We've overcome that, and he now views me as the leader and does everything I say, until he sees any other animal, and sometimes people. In the one situation where an unleashed dog ran up to us, he didn't bite, so I think the barking is out of fear if anything, but I worry that in another time maybe he would be aggressive so I've strayed away from virtually all socialization and I don't want it to be like that.
When something triggers him, he suddenly stops listening to me at all and I really need advice on how to deal with this, because he loves car rides and I'd love to be able to take him out with me any time I'm out running errands or just going for a stroll at the park. Any advice others could give would be amazing, and I'll gladly provide answers to any questions if needed. Thanks all!