So I've been doing a lot of research on this very topic. And even though I raised many dogs in the past, I was a total newb to this issue. Speaking with experts who do this for a living for 30 years, there is no way you can calculate how a puppy will protect you as an adult. The ONLY thing to look for is 1. Genetics and 2. drive. As a pup they only have prey drive, make sure the pup has this because you can turn prey drive into different types of drive as they mature. Genetics is the most important part. So you should look at the parents and the pedigree. I would pick a working line pup with tons of drive if I was looking for a protection prospect. And then you have to really not screw up the training for the first year because you can ruin a dog for life just with a stupid "experiment" that may pop into your head. DO NOT DO ANYTHING besides play with the pup to build drive (tug, fetch, tracking is great to teach the dog to work for you), and light obedience. Too much obedience kills their spirit. This is what experts have told me anyways.