Defending Against Zombies - Defense in Depth

If you want to protect the old homestead against zombies, you need to have multiple layers of defense.  As season 6 of The Walking Dead shows, a single layer of walls is not enough.  Instead, you need to be able to fall back to defensible interior positions.

Château de Sully-sur-Loire, Loches, FRANCE - Photo By Christophe.Finot (Own work) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons

Think of the medieval castle as a model for fortifications.  A typical castle was protected by a moat, by exterior walls, by towers, by interior walls, and finally by an innermost defensive keep.  Beyond the castle model, you can also think outside the box.  You can also be protected by multiple defensive concepts such as concealment, alarms, walls, and escape routes.