My set up is similar to feldar - I have a pen (20mx10m) that's dug down to 18 inches, and is seven foot high with an overhang at the top. It means I can leave them all inside the run when I'm not around and then they can free range when I am. I was getting quite relaxed about the free ranging and leaving them out while I popped out for a while but we've now seen so many foxes by day and our neighbours have lost two lots of chickens to foxy, I'm now being really careful. Inside the run we have the houses so they're all locked up at night.
I'm getting a new run done and because it's so big (70m by 45m), I looked at electric fencing. The most reliable is to combine a tall fence with several strands of wire a foot or two out from it - one just above the ground to stop digging (then you don't need to dig the fence down as far but you do have to keep the grass down so it doesn't ground the wire), one at nose level and one higher up to stop them climbing over. I think if you've just got the poultry netting, a hungry fox would eventually work out it could dig under or jump over.
You don't mention whether you'll be able to shut the chucks in at night? That's when they're most vulnerable. It's really just a question of balance. My neighbour goes to market, buys cheap, hybrid chickens and is not too upset if the fox grabs a few. I've got rare breed poultry - chickens, ducks and geese - which have taken some efforts to assemble (including a ten hour drive coming up tomorrow) and there are some in there that I would be devastated to lose. If you make a purely cost effective decision and just want eggs, buy cheap hybrid hens and see how you go with the poultry netting. You'll soon know whether you have a serious fox problem or not...
H