That level of security is probably directly proportionate to how close a fence hopper is to a flight line and a fatal interaction with an aircraft either landing or taking off. Security would also be inclined to stop and question people who obviously (key word) don't belong.but I couldn’t comment on whether you could sneak in or out of there undetected because I’m not very knowledgable about the security beyond that.
But....other than being around a flight line or obviously not belonging, once somebody is "in", they are not likely to be bothered by security so long as they blend in.