So different opinions already
Free ranging is always a risk, and twice over our 20 years of keeping hens we have had a group of hens killed during the day - both times by foxes released into the country from the city
Our decision has been that the benefits of total free range (locked in at night) far outweigh the risks. That's our decision.
When we first got hens many many moons ago, we spent ages making a lovely huge pen for them. Within about 6 hours they had all flown out
- our mistake.
Now when we get new hens we shut them in one of the houses on their own (our henhouses are 6' x 8' garden sheds, so plenty of space, and well ventilated. Then we open the pophole for a short while in the evening. The first time one or two will step out then scuttle back in, but each day they get braver until they're all out and about all day.
Our hens range over about 3 acres - there is plenty more ground, but they choose this area. For some reason they don't go beyond the march fence, and only one went on the road (and was rapidly an ex hen
) So from this I feel yours may want to wander further than your acreage.
In that case, I would vote for a very large enclosure, with mesh sides, the wire dug down below the surface so foxes can't dig under, and netting over the top, to keep hens in and birds of prey out. This type of enclosure is helpful, but not foolproof, as badgers can dig or rip through your defences, and foxes can jump, stoats squeeze through anything. Ideally, you should be able to move the pen whenever it gets muddy, to rest the ground and prevent worm build up.
Once you really get to know your birds, you can decide whether to let them free range further.