You need a decent sized dog that will bark at something that comes near your house. You don't need an actual dog to bite someone. You aren't training a "guard dog" without serious professional assistance. Any dog trained to attack for any reason is a MASSIVE responsibility for both the dog and owner. You need the right dog for the situation. You are not anywhere near knowledgeable enough to pick the right dog, most people aren't.
Now if you want a dog to sound like he's going to kill you, all you need to do is train him to bark when he hears anything outside. A larger dog is key. Pit Bulls are awesome with kids, as are american bulldogs, mastiffs are another good choice. Shepards will naturally go nuts when they hear anything outside. The bark from a doberman will make almost anyone who is trying to break into your house shit their pants. Chows are phenomenal guard dogs by nature, but they are known to not be as good with kids.
You need a big dog, and with a big dog you need to diligently train the animal or your life WILL be miserable. Call a well reviewed VET and talk to them about the shots the dog will need. Rabies and Distemper are typically the minimum, but it can depend on your municipality.
#1 thing to remember is make sure you can afford the animal, that includes all of the medical bills associated.
Edit:
My friend has an American Bulldog, Pitbull/Rot Mix, and a bull Mastiff. You don't get within 50' of the house before you know not to walk any further. They aren't any threat to anything on 2 feet, they have dragged down deer before though, and a coyote. Cleaning up after that was disgusting. 2 guys below are 150 lbs approx. The mastiff is only a year old, she will top off near 175-180 though.
