I have both light and heavy hens - the highest I have seen then fly is around 3-4 foot, but that is not to say that they can't go higher!

The usual recomendation is for at least a six foot boundary, this should have the added benefit of minimising the number of foxes that will now home in on you! To be truly secure you need to either bury a foot or so of the fencing or slab/pave around the border of the garden, lapping the fencing wire under the slabs to stop Mr Fox getting in and unfortunatly foxes can climb so the fence will either need to have an overhang (leaning out) at the top or some other method to stop Mr Fox such as a roof!

I accept I'm slightly paranoid - Mr Fox has been trotting down the garden and sitting at the gate into the hen run!

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The weeks and the years are fine. It's the days I can't cope with!