Okay, if I understand what you want, you want a dog for protection. If that is what you are going for, you need to buy a dog that is trained for protection. Contrary to popular belief, most dogs will NOT protect their owners if they are not trained for that situation. Look at it from a dogs point of view. Dogs are ruled by instinct. Instinct tells a dog it has two options. Fight or flight. In the dogs mind, flight is just as productive as fighting, and even the best bred dog therefore has only a 50% chance of defending you. Furthermore, if you DID buy a dog that is that ferocious that it will always attack, it is going to have a very unsound temperament, and is just as likely to attack someone you DON'T want it to.
Onto the breed choice. Labs are not known for their ferociousness. There are a couple out there, but most labs are going to walk up and wag their tail at intruders. Working line German Shepherds are a really good choice. :) (They are my breed of choice). Rottweilers, Dobermans, and Malinois are more good choices. Just make sure you look for WORKING line dogs. Show line dogs do not generally have the termperament to be protection dogs.
Finally, I would look for a fully trained protection dog. These are not cheap. Usually $5000 to $10,000. However, the proper training is not cheap, and takes a long time. If you need protection soon, you can't wait for a puppy to grow up and get properly trained. When you look for an individual dog, look for one that is not afraid of anything, and make sure whatever breed you get, it has a health guarantee. Also, look for a dog that has high drives, and most importantly, a dog that you can get along with. A dog tends to be more outgoing and aggressive, but a female tends to bond more with its family. Some females are a force to be reckoned with anyway. So gender is really a personal opinion. I don't know of trainer/breeders in your area, but I would try searching online.