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.
You got the upvotes but no engangement up until now. Allow me.
To my knowledge, the kink doesn't imply deriving into actual pregnancies. Yes, the most orthodox people making this their fetish will argue that the thrill is in getting to a pregnancy but still. Many can enjoy the kink with no real consequence, using birth control, and I've read that even gay men can have this fetish to a degree but it is then called cum dumping.
So, perhaps we could be a bit broader on the subject?
Are we speaking of true impregnation fetish or just the fantasy play with a lot of creampies added for extra fun and visual effects?
Now that I even think about, I can come up with an easy game to spice things up, if the whole breeding fantasy is a thing. Consensual adults required and additional birth control.
Get a box of condoms. Open it and dump the condoms on a surface. Mark every single one with a large X or some other sign, in sharpie. Pick a few of them and, with a very thin needle, poke them through in such a way that may cause rupture. Put the condoms back in the box and keep it secure, if you fear some person not into your kink taking a few. Organize a roleplay night and use one or more of those condoms. Get really kinky. If one ruptures, bonus points for the kink roleplay.
This should only be attempted between informed knowing and consenting adults. Otherwise, purposefully damaging a condom can be considered rape.