All good points about socialization but I think you are putting too much on the dog. dkoriss is probably right in that no socialization will create the ultimate guard dog. However, as I stated, society demands that in an urban environment dogs must coexist with people and be approachable. There is a fine balance between socialization and ultimate guarding abilities.  Ultimate socialization results in minimal guardian abilities simply because to "trust" strangers is anathema to guarding. Balance is the best case.