Rolls of razor-wire, any TA people still going ( given a CLEAR set of R of E ) and more night-capable cameras around would seem like just a start...the chap in the last incident seems to have been a random nut - sorry that's not very PC but anyway - what if he hadn't been...
Probably inside the minimum range of a Stinger, but an RPG would have been an unpleasant beginning to one's holiday - this is where the much maligned 'spotters ( and no I'm not one ) are very much a benefit to our side and to be encouraged - sort out bona fide ones and give them tours of the aircraft etc, and a direct security number to call - if necessary tell them there's a Concorde test flight coming in sometime !!!
Anything except rely on any version of the police " sorry I shot you repeatedly but you WERE reaching for a notebook - now how's my full pension coming along ? " - when I worked at test ranges the guards were armed Military Police, and a regiment of regular soldiers were living rough, unseen, in the bushes.
Considering the change of priorities, I would hope they ( if not busy in Afghanistan ) might be on their way to various airports...