We dug trenches and buried 1 x2 welded wire. Goes down 14/16 inches and then comes out another 8 inches. Works well to stabilize lighter structures in windy locations also. We knew we had every chicken eating varmit around and wanted to make it tough enough that they couldn't get in in a single night. Wish we would have put in drainage at the same time though.
i would have buried the wire deeper myself, except we built the coop in July when the ground was rock-hard -- and, when i did research on-line, there didn't seem to be any consensus as to which is "better," wire that goes down into the soil vs. wire that just extends outward -- i think they are equally good.
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