The days of the naughty field are gone I'm afraid
Not at all. If you have private land ( say, a garden or a field ) near a display then the 'authorities' can do nothing about prohibiting others from using that land with your permission. Short of going to court for an injunction. After all, I might just happen to have my birthday on the same day as Farnborough's public show and have invited 70 friends around to celebrate...
Accessing such land might require turning-up before road closures are imposed but most enthusiasts won't find that a problem.
Well, at least that stops people watching an expensive-to-put-on airshow for free!
Most naughty-field types just won't go in that case. Viewing from inside the show is usually worse, plus all the hassle of those annoying children and wailing commentators. Or vice versa.