What you probably are looking for is a nice black or black and tan, 60lb pet that barks a lot. The shelters are loaded with them because it is a proven fact they are last dogs to get adopted out because of their colour, they look scary.
You just need a dog that looks the part.
Even if you were to get a protective breed it is likely to run away in the face of danger and leave you standing there to defend yourself. It would need to be protection trained and having said that very few have the temperament to even be considered for protection training.