Nothing - no dog, or alarm system, or firearm - can keep you completely safe. Your goal, cynical as it may be, is to be less vulnerable than someone else so the BG finds easier pickings. It is, for example, much more likely that the BG who is scouting you will decide to go to a house without a dog than that he will come up with an elaborate plan to silently kill your dog. BGs aren't looking for a challenge, they are looking to enrich themselves with the least effort possible.
And although they haven't been on TV or been the designated spokespersons for their department, I have several times had LEOs tell me that they recommend citizens, and especially small business people, be armed. Preaching to the choir, of course.