I don't know much about training, so I can't comment on which methods work best like other commentators. But I can confirm that anecdotally obedience training,

I don't know much about training, so I can't comment on which methods work best like other commentators. But I can confirm that anecdotally obedience training, at least in some forms, is like magic. We adopted a shelter dog, so she came with a slew of emotional scars. She started showing signs of potential aggression, and apparently was on her "third chance" from the shelter already. We didn't want her to have to go back yet again, nor did we want to risk anyone or her getting hurt. So we searched around and found a trainer. Again, I don't know what "method" this trainer used. But it was a single (expensive) session, 1.5hrs long, in our home with a former K-9 trainer. Afterwards it was like flipping a light switch on her. She no longer barked/growled/lunged at passersby or even other dogs. She's perfectly calm around other aggressive dogs. She won't leave or enter through doors without our permission. We can stop her dead if she chases after an animal in the backyard. And it's not just us; our vets continually re-affirm how much better behaved she is while with them. All that after one session and continued re-enforcement from us. We also crate trained her, so sleep isn't an issue. That was another amazing transformation; going from crying all night to getting up and leaving the couch for her crate when it's past her bedtime and looking back at us like "you guys going to bed or what, geez!" As for separation anxiety, which she definitely has, I came up with my own technique for that. First, we stopped crating her when we left. It caused her too much anxiety. But that didn't help completely. People suggested playing music, but that just made her more anxious as well. As did giving her treats before leaving. The thing that really worked: before we leave I just talk to her and tell her that we're leaving, tell her if we'll be back "soon" or "later", and tell her she's a good girl. It's weird, but after a couple times, it now works like a charm. She definitely doesn't like it, but she immediately settles down and lets us leave without trouble. And she doesn't wreck the house while we're gone. I'm not sure how much of what I say she "understands", or what part of my magical incantation is actually salient. She has an incredibly accurate sense of time, so I figured she might be able to correlate "soon" or "later" to how long we're gone. Hopefully that's communicating some expectations to her that help her be less anxious. It's amazing the transformation a little training can do. To go from an aggressive shelter dog on her third lease on life, to one of the better trained puppies we know is an incredible journey.