I hope I'm understanding your angle of approach on this.

Crowd control dogs are highly trained and don't go out on a rampage unless commanded to. It's their handler that triggers the response. Otherwise, the dogs do not exhibit arbitrary aggression behaviour. Even military trained dogs must not demonstrate aggressive tendencies; if so, they would be a danger for their handlers and other allies. The attack behaviour is developed and triggered under specific conditions and commands.

You can train a dog in the same manner. Dog trainning is an open knowledge base and I personally think everyone should work with their dogs in order to give them the best outcome possible for their lives. It's the closest symbiotic relation our species has with another, in my understanding. And it's fun.

From this point forward, I'm going to talk from personal experience.

I was lucky enough to have the perfect dog in a very bad point of my life. That dog forced me out of my house, to go on long walks and think on something other than my misery. I never taught a single thing to him beyond sitting and laying down on request. I never taught him to wait for me, keep an eye out when I was foraging for something or being protective of my family.

This was dog that, still not fully grown, took on two other, bigger than him, to protect my infant child, out of his own vollition. And that when called by name returned. This would be the same dog, that years later, would stare down another> , known for being unreliable around children, into submission, a dog the person responsible for feared and kept chained. I had a lord by my side and I was lucky for it.

When that dog died in my arms, of old age, I lost a brother and a son. I'm crying as I write these words.

Today I have two dogs of the same breed but I have severely failed them, by allowing another person to force me to take them to under the wrong conditions: separatly and too early. This created a vicious beggining for their lives, making them fearful and wary of everyone, which made them prone to be aggressive out of fear and aggressive towards each other. Things have been better with some measures but I feel as I failed them.

Most dogs show aggressive behaviour out of improper care, be it by negligence or abuse.

I've been studying and working, actively, to be a dog trainer. I have scars, from my own dogs, for mistakes I've done. I hold no anger against them. It was my mistakes that made them react to the world as they do today. I've helped other people not make the same mistakes with their dogs; it's my small contribution for a better world, I hope.

I've only met two dogs beyond any reach. One diminished from birth causes, making the dog effectively uncapable of acquiring any modulation to his behaviour; besides eating, nothing mattered and he would attack anything he viewed as potentially edible and attack to keep others from food, even after being fed to satisfaction. The other had been severely abused, being given alcohol as a pup, which stunted his development, both physical and mental. The dog would attack out of nothing, anything, and would not calm down until passing out of exhaustion. I believe he suffered from allucinations. Both had to be put to rest, as their lives would never be happy.

So, you can have a dog prepared to defend you. You just need to prove you can take care of the dog properly.