I know this is popular advice, but...I think that in many cases getting a dog is useless, if not worse. Owning a dog capable of protecting you involves assuming a fair amount of liability for its behavior toward others, as guard/protection dogs are trained to execute aggressive/hostile behaviors. True, the conditions under which these behaviors are to be seen are supposed to be controlled, but the potential ALWAYS exists where a guard/protection dog can inappropriately attack an innocent person, such as a guest or even someone in your household.
Further, a home intruder who knows what he's about can fairly easily disable/destroy pretty much ANY dog - I don't care how vicious the dog is. Personally, I see a dog as just another thing in the house I have to protect.