I agree with what Chrismahon says, but remember, it's not just keeping the hens in but keeping predators out, that's important. To exclude foxes, dogs etc from a fenced and open-topped run, you need two-metre high fences, preferably with electric backup if it's an open field. If the run has a mesh roof, you still beed it to be 6ft so you can get inside without crawling in poo!If it's a low enclosure that you can step into, perhaps on a lawn to keep them off the flowerbeds, you need good perimeter fencing to your garden, because even if you were out there with them whilst they were in the enclosure, they are still at risk if a dog suddenly comes into the garden and goes for them, as I found out recently - luckily mine were shut up at he time, and I've now installed a high gate at the weak point in our boundary. It really depends on your setup -confining hens in a garden is different from keeping hens in large runs, like the ones Chris was talking about, but their safety must always come first.