I don't think it's contrived compared to the expectations that ordinary people have of their dogs. Dog owners likely secretly think that their pooch is going to protect them, even if they're not protection dogs.
What you need is an aggressive race. Also females tend to be more protective AFAIK.
I had a Rottweiler for example, that I was walking without a leash near my building because to my knowledge she was well behaved, but with no special training other than me talking with her daily. So one day I was attacked by a homeless person and my dog, came from the bush where she was peeing and nearly bit his hand off. Well she was about 50 Kg and size and weight do count.
And another day she stood her ground to a pack of 3 or 4 street dogs. What can I say, was living in a bad neighborhood.
Also in our country we still have many classic shepherds that practice transhumance, with these 2 races of dogs being very popular, called "mioritic shepherd" and "caucasian shepherd", including all kinds of half breeds, and these shepherd dogs can get pretty big and get used for defense against thieves, wolves, you name it.
And they don't need training btw. They aren't kept for emotional support, they are kept to defend the herd and with the harsh conditions involved, they can get really, really aggressive. And actually it's the same story if you go to the country side where people keep dogs to protect the house and livestock. Dogs being entirely utilitarian, they only get food and shelter in exchange, not love, so they know what needs to be done in case of intruders.
My grandparents had a saying — if you want a dog that can protect you, you should never allow other people to feed or pet it.
Interesting that you'd say this -- I think there's always exceptions to these rules, and here's mine:
I had a half-laborador, half-pitbull. Like a lab, she was very aware of people's emotions, and like a pit, she was strong, aggressive, and had a very high pain threshold. (She barely reacted when we pulled porcupine spines out of her nose with pliers.) Unfortunately, this was a problematic mix. If I was the least bit uncomfortable with somebody, even if it was just social anxiety and I wasn't in any danger, she would start growling and try to make them go away. And she viewed every other dog as a mortal threat, to which she would react with murderous fury. I have no doubt that if I had felt physically threatened, she would have done serious and possibly disproportionate damage.
I wasn't able to take her out much.
What I wanted to say is that you'll have a much higher probability of success with a race that's known to be aggressive, if that's what you want, then with a race that was bred as a companion dog. And half-breeds can be very aggressive or very friendly, but it's essentially a lottery.
One day, he was out walking her, and three guys came up to him. They stood around my friend in the usual threatening triangle formation, so no matter which way he faced someone was behind him. They started accusing him of stealing from them, and started to get aggressive until one noticed his dog and asked if she attacked. Just a moment later, she launched herself at the three of them - only the tight leash saved them from being bitten. She'd die to protect her family.
Whenever I visit him, she "attacks" me - launches herself at me so I can lavish attention on her for as long as possible. If he ever had to get rid of her, I'd take her in a heartbeat, but depriving her of the kids she loves so much would be one of those heartbreaking moments you'd never want to see.
Let children and elderly pet/feed and you suddenly have a well behaved protection dog.
Funny enough the resolution is for the alpha to scold the vacuum in front of their dog(s) thus re-establising pack order.
I had a locksmith come to replace the ignition switch on a car, because the key couldn't turn it any more. It took longer than I expected, and finally I decided to use the restroom. Of course, that's when they locksmith finished his work, and came in to tell me he was done.
So my dog sees this guy walk into my house without me there to meet him. The dog, essentially, drew a line in the carpet and said "Don't take a step across that line." It was impressive. I didn't know before that how my dog would react, but she seems pretty... sensitive... to people coming into my house when we aren't at the door.
Definitely not good guard dogs.
There are two greyhounds, not three.
If I was downvoted for saying that greyhounds aren't good guard dogs, then whoever did that should probably actually meet some greyhounds. The muzzles they wear aren't to stop them biting people, they're to stop them nipping at each other during races, and to protect small dogs and other animals when they're not racing.
They're sight hounds - silent watchers with an unbelievably friendly, trusting, and loving nature, and once they've tired of your attention they will wander away to sleep off the excitement.