Saw this article today on Mother Earth and am astounded by the brilliance. Not really for the lazy gardener or tiny flock owner, but it is just fantastic. The writer calls it the "Chicken Moat"
http://www.motherearthnews.com/Sustainable-Farming/1988-05-01/The-Chicken-Moat-Enclosure.aspx
http://www.motherearthnews.com/Sustainable-Farming/1988-05-01/The-Chicken-Moat-Enclosure.aspx