This is an interesting question. My husband and I were robbed shortly after arriving in Brazil. Afterwards, everyone said, "you have to get dogs". We ended up with 3. Two mongrels and a Brazilian Mastiff. We consider the two mongrels the noise makers and the Mastiff as 'the protector'.
Mastiffs have a built in instinct about protecting their family. Ours weighs 48 kgs and is a lot smaller than his father is. When people know you have a Fila, as they are called here, they are hesitant about entering the grounds.
Besides the Fila Brasilero, the Doberman, The German Shepard, The Pit Bull, and the Rottweiller all have restrictions when they can be on a public road. There also has to be a sign stating that you have a dangerous dog on your property.
That said, I use to have a Laborador who was very protective of my children, even with people he knew.