At Cranfield you use to need a separate pass to get at the aircraft, freely issued to pilots on arrival but otherwise you had to pay extra, which tended to keep the idly curious (and their kids!) behind barriers.
At one PFA rally, I was sat at my stand quietly editing an error-ridden draft of some technical document or other. I left it on the table whilst I went to the loo, and when I came back somebody had nicked it - so they got some free bad advice and welcome to it, created work for me though.
G