I would want a dog based on the following characteristics:

Smaller than average. I won't be relying on the dog as a primary defensive tool, so no attack dogs. Also, smaller dogs require less food to maintain.

Built for the outdoors. Breeds that are primarly outdoors dogs.

Herding dogs. They have more intuitive sense of how to act around other animals. They don't just go after and engage threats, but will alert on them, and they won't just chase down game but will try to control them. They understand teamwork pretty easily. They seem to be able to read human actions and intentions pretty well, including strangers. They make excellent guard dogs. They travel well. Most are good with familiar children.

So for this scenario, I think a GSD or a Border Collie or even an Aussie Shepherd would be ideal.

If security were more of a concern, I might go with an Akita. They are a little more guardlike, but still have decent field sense. They can be a bit too aggressive with other animals, though.