Lookouts, sentries, and guard-duty

[Tartar Horde]

The Romans famously used Geese, but you simply can't beat the Dog. I would trust a well trained dog to detect an intruder than the best Ninja. Your Dog will protect you with it's life if it has to, Mans best friend for a reason. The Dog was the first animal to share our campfires, help us in the hunt, and guard our tribes, long before all other creatures. He was with us in the last Ice Age, thousands of years before agriculture and all the other domesticated animals, your best mate.

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I don't see any problem with using an American frontier analogy, no more than I would Sun Tzu or Frontinus(the Art of War/Stratagems & Aquaducts) the principles are exactly the same, even if you are in a suburban English house.