The only problem with open topped fences is that sometimes foxes can jump/climb over them
As happened to me a few weeks ago.
Neighbours at garden's end built decking, a greenhouse and water butts along the 7ft chicken fencing. Mr. Fox just used the water butts to clear the fence - ho hum.
I've five chickens now and getting another 5 (maybe more) and the fencing has been beefed up - guard towers, mined area, trip wires etc.
Anyone looking to rehome chickens could do worse than give the charity Edinburgh Cyrenians Farm a call (0131 333 5202) and ask for Tom. They're organic chooks that are getting "a bit long in the tooth" - pun intended and I think they're selling for a fiver.