Taking that theory to the extreme; (and not really a genuine suggestion, but....) rather than air fences, why not put chicanes before the known danger points. These could be removed right after the races.
(Howls of horror and much wringing of hands!!!)
Drop the lap speeds to 100 at best, all use short circuit gearing and still have a good race on the Island.
Be a lot cheaper than 37.73 miles of air fencing.
I wonder if anyone has the accident vs injury stats for somehwere like Castle Coombe before and after they did this?
Forgeting tradition for a moment, would it work?