I think any fence anywhere inside the airfield area (by that I mean within 50 yards of the peritrack) is actually a flight safety hazard at Kenley. Anyone who knows the site realises that it is actually fairly small and the DLA is actually close to the peritack itself in some launch/landing directions and also that the trees and undergrowth and buildings actually mean that there is no real undershoot option in a lot of cases. This means you have to land on the airfield - or nowhere at all. Putting up a fence effectively introduces a hazard to the operations. That is why the fence (and it is required IMHO) needs to be set away from the peritrack - hence my earlier comment (slightly tongue in cheek) about the AM boundary blocks being a suitable demarcation line............
A 'viewing area' could be created at one of the ends of the site (say Kenley Common end) and this could allow people to watch the gliding (without risking their or the Pilot's necks) and stay safe.
From a safety perspective the operations are no less hazardous than any other airfield, we wouldn't let people walk over Coningsby or Marham so why Kenley ?
Just my 2 pennyworth............
Arc