It's not just actual attacks that harm chickens; fear and stress stop the birds eating and can open the door to other problems. Unfortunately the goshawks in this area have a penchant for harassing my birds even with the pens fully netted. Indeed yesterday the goshawk didn't fly away until I was about ten feet from it. The chickens were almost injuring themselves trying to hide.
I realised it was time to give them some extra cover. So I wheeled the ancient barrow into the pen, and also rigged up a corrugated iron-roofed shelter using some cut pine logs and 2 spare planks. The roof is screwed onto the planks, which are long-nailed into the stumps; it's not going anywhere.
While it took the birds a while to get comfortable with the new arrangement, they were soon happily perching on top of the obstacles and also checking out the under-side. If the goshawk comes back, at least the birds will have a visual barrier between themselves and the eye of doom. As for the goshawks, they'll never leave the pens completely alone. But at the moment, as long as the netting stays intact, they can't get in, and even if something tears a hole in the netting the birds have got some chance of evading the talons.
I don't know if these things would work on free range, but it seems to me a goshawk would have a lot of trouble chasing prey under a low roof. If I ever free range again, that's what I'll do.