You don't need a trained, protection dog. E.g. Labradors are toys, being bred to be playful and loving. A half breed of a pit bull doesn't count much either.

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.