I just purchased a coop yesterday and next weekend I need to get the run made to get ready for the arrival of the birds. My questions is how high do I need to make the fence? I was planning on getting some 8' 4x4's and burying 2 feet of them leaving 6 feet above ground ... does it need to be this high? Or could I get away with 6' 4x4 burying a foot leaving a 5' wall ... or possibly shorter? Thanks!