As everyone already knows, dogs are pack animals and there must be a lead dog. If a dog is showing signs of fear or dominance then it's confused about who is leading the pack and that fear or dominance could simply be the dog acting out because it's being forced into being the pack leader. When there is a clearly defined pack leader then the entire pack behaves as expected.
The pet parent’s number one resource for dog training and dog owner advice by world renowned dog behaviorist Cesar Millan.
www.cesarsway.com
I'm very sorry you've been mislead by a charismatic celebrity with a great PR team. It's a real shame he was given such a big platform by a channel that once promoted educational, science-based content, and that Nat Geo has continuously ignored pleas by reputable experts and organizations specializing in animal behavior to stop promoting his outdated and sometimes dangerous methods.
Dominance theory begins and ends with an 80 year old study where unrelated wolves were thrown in a stressful, unnatural situation (ie a pen/enclosure smaller than what even one wolf pack would have as a territory), reported on by researchers who were incentivised to find some kind of hierarchy in their behavior. This was then assumed to be true of dogs, who despite being physically and genetically very close to wolves, are significantly different behaviorally. And then there were further assumptions that intra-species behavior will be exactly the same as inter-species behavior - IE that dogs think of us as other dogs and interact with us socially exactly as they would with other dogs.
Every modern study has shown that wolves form family units - no alphas, just parents and offspring. Current research suggests that dogs, left to their own devices (ie feral and pariah populations), form and dissolve loose alliances with other dogs based on their current needs, but do not have permanent packs or leaders, nor do they form family units like wolves do. Multi-dog households are a little less 'natural', as our pet dogs don't get to pick and choose which dogs they spend the most time around, but they still aren't hardwired to conform to some strict social hierarchy.
Dogs do tend to thrive better when they have boundaries and clear expectations, no argument there. I mean, don't we all? But this dog is terrified. Maybe it's genetics. Maybe he's had a bad experience with a leash, or collar, or someone bending over it. That doesn't have to be abuse, of course, could be as simple as he never had a collar introduced positively, or he's just so overwhelmed that something slightly worrying/uncomfortable is too much to handle. Caleb, he needs time and space to decompress from the shelter, positive exposure to the leash and collar, and gentle desensitization to having his head/neck handled. Leaving a short tab or traffic handle on him is a great way to avoid having to put him through something he finds scary as much as possible until you can work through his issues. And just bonding will help. Silly games, simple tricks, just hanging out and letting him know you won't hurt him and respect his limits. He's been through a lot, give him time.
