I'm in the same boat. I could only take him to the office if I would work there alone. He turns into cujo with almost all dogs or puppies, with golf carts, with men, with children, with motorcycles, and crows...gawwwd. We did the same thing, consulting our vet, had him on holistic meds, trainers, behaviourists, etc., and it's still going on.
I made one observation though, through a neighbour (moved away since
) that had one of the biggest golden retrievers I've ever seen: Tucker. We met by chance when I was walking outside our complex (nice little hiking paths) and he came towards us....all I thought was holy shit, here we go, let the drama begin. I tried to somehow dodge them, but he beelined straight at us.
Whe I told the neighbour that Rohe is a bit "iffiy" with other, bigger, new dogs he meets...iffy my butt
... the neighbour kept his cool, and just said, they will be totally fine, and that I shouldn't worry. They sniffed, jumped around each other, and we walked for a good while next to each other. Tucker and Rohe became the biggest buddies. Tucker came to our apartment to pick Rohe up when he went for a walk....craziest thing I've ever seen. The neighbour lived here for 3 years then they moved away. So sad for Ro. Now, he has 3 other dogs on the complex he is happy to see - they are different sizes, different breeds. Every other dog, he wants to go crazy on.
What all the dogs had in common was the very positive energy, kind energy of their owners. The owners were all different ages, sex, and cultures. But they all had the same aura if you will radiating from them. And that's what he felt and still feels. There was/is something about them that totally calms him down...and their dogs are rather calm and gentle themselves.
Also, my vet told me that Ro is really a scaredy-cat, and that his first instinct is to turn into cujo to frighten away things, people, and other dogs. And that if the other dog is calm, non-reactive to the drama Ro is creating, Ro will be able to calm and trust himself. And that even if a dog and dog owner seem calm and friendly to me, Rohe's perception und understanding of the signals they give off, is much deeper more detailed than I can see or imagine.
So truly, hell, I don't even bother anymore, if he feels the need to bark at other people, or dogs, I just calmly remove him from the situation, even though he acts like the devil on a leash. It's these "hidden" signals - sometimes a flick of an ear, tail being high and not levelled, eye contact, the smell of the other dog, that can trigger reactions. A dogs nonverbal communications is the most faszinating thing to me, and even if I can read and predict Ro's behaviour pretty well, I'm sure my human brain and eyes, miss so much, that he obviously picks up and reacts to.
Dogs have really their own characters. Almost all my dogs were rescues, and Dexter for examples was everybodies friend, you talked nicely to him, he would follow you home. Roxie, hated cats in general, white cats specifically, or white dogs with passion. Don't ask my why. When we encountered a white dog, we found ourselves walking on the other side of the complex, or street, or town...LOL. But all my dogs, surrounded by their family and friends at home, being with their pack, were/are the sweetest, nicest dogs you could ever think of.