This dog came from an animal shelter and my friends suspect that it had a rough time on the streets with other dogs. That's probably why it had abandonment issues and had to act all tough to fend itself against other dogs. My friends take a patient but firm approach raising the dog. Sometimes they get frustrated but they never give up. So far they have gone through a few dog trainers and are starting group lessons for problem dogs soon. Apparently the dog's behavior has already improved since they first brought the dog home, but they still have a long way to go. One of the trainer told them (paraphrasing a bit here), "With the right techniques and patience, you can re-program any dog."
When my friend's dog is around its owners and other human beings, with no other dogs around, it acts completely happy and relaxed like a normal dog. You cannot tell there is anything psychologically wrong with it. When another dog shows up, it's as if the dog is programmed to go into anxious attack mode. Kind of like how some innocent phrase that my mother says in a casual conversation will send me into an automatic defensive/anger mode, with me scratching my head afterwards at why this is the case. Or how I automatically cower at the presence an unfriendly, rude, and demanding person when I ought to be able to defend myself now as an educated, informed adult. Looking at the dog, I see that deep-seeded behavioral patterns are deeply ingrained and will take a lot of patience and persistence to be re-programmed. I must have faith that with my eyes now open, my efforts in re-programming myself will help me get past the emotional wounds that I didn't even know I've had.