A couple random thoughts about dogs.
Do not take the easy way out when buying a dog. Buying a dog locally out of the newspaper is a crap shoot. Yeah, it is easy and quick, but usually is a mistake. Don't even go look at them; it is almost impossible to resist the puppies. This is of course, unless you have researched the breeder and bloodlines of their dogs extensively prior to going there and they just happen to be local to you. I have found that you can buy a dog from a nationally known breeder with proven blood lines that are guarenteed as to temperment and health for the same money as people sell puppies for out of the newspaper. Do not buy a dog unless you have proof of the parents health certifications; hips, elbows, eyes. There are a couple reasons for this. #1, I am a dog lover. It would devastate me to become attached to a dog and have it die young or me have to put it down before it lives a long and happy life. #2 If you are serious about this, you are going to have a lot of time, and some money tied up in this whole affair. Not only do you want to have a dog who's health allows it to do the things you want it to do, you want to get a solid return on your investment and not have health problems limit it's effective life. Think about this like you would think about buying a gun. If you were buying a new gun to defend your life and for your own enjoyment, would you rather buy a gun from ______ (Glock, Colt, S&W, Bushmater..........) or would you rather buy one from this guy you heard about on the other side of town that builds them in his basement ?
AKC "papers" mean almost nothing. Nothing that matters.
Buying a puppy from bloodlines with titles is a good indicator that the dog you are buying is intelligent. There are no guarentees, but this is the only real way we have to judge the dog as a puppy.
Saying that American blood lines are worthless is painting with a real broad brush. There are certainly good American blood lines. However, as a general rule, Americans take shortcuts in everything, and are far more concerned with money than quality.
You specifically used the words guard dogs. THis means different things to different people, but to me, this doesn't mean owning a dog just so it will bark when TSHTF. This means that you probably want to buy a dog from the working breeds, preferably from a bloodline frequently containing Schutzhund titles.