The electric netting is interesting, but I can't see the benefit of making it large. My experience with the cornish has been that they don't spend time in the sun unless it is early morning. So, if you have the shelter inside the netted area, that is where they are gonna spend their time no matter how much room they have to roam. You will probably see poop build up under the shelter, next to the waterer and feeder, as that is where they are gonna spend their time. Also as a side note, in my experience, when the sun is up and it's a hot summer day, birds will not drink from the waterer unless it is in the shade.
As far as predator birds, no age is immune to being snatched. We had a large bird die this fall. Probably weight 7-8 lbs. My father-in-law took it to his farm and threw it ont top of their chicken compost pile. Well, a fox took it the next day, and right before getting to the woods, a Bald Eagle swooped down and took it from the foz and flew away. I swear this is not made up.
We raised just under 1,000 cornish this season. We used Salatin style daily move pens. Ours were 10x12 and 30"tall. We put about 100 birds per pen. At the peak, we had 6 pens going at thesame time. I am probably biased, but i dont see a better way. The pen is great b/c it provides shade, dryness, and protection from predators. At the same time, it still allows sunlight and air to come into play. And, unlike a fixed building, you are not allowing waste and PATHOGENS to build up b/c you keep them on the move. The fact that they are only gonna range so far, makes 10x12 a logical size. Some people knock the fact that this breed of bird is not gonna run around and forage all day, but my response is: who cares. They devour all the green matter that the pen occupies for that day, and get to do that everyday of their life. And they eat a non-soy, organic feed.
The only negative is having to move multiple pens. Everyday. For 7 months. That is why i say the electric netting is interesting. I am just unsure, in my case, if it would be less work. The 10x12 are just too efficient. We just need to improve our pen construction and how we physically move them. I have a dolly like salatin uses, but find it to be a royal pain. We use 2" PVC pieces as rollers at this point. Plus, we have birds anywhere from 2 to 9 weeks old going at the same time, so we would still have to have a series of fences and shelters...