Truthfully, it is an impossible job to accomplish - too many people (ramp, maintainance, cleaning, construction, concessions...or the security folks themselves!), too many entry points, too much 'fence-line' (remember the pair that 'rowed their boat ashore' at JFK a few years back? Then wandered around the taxiways and runways until they were spotted?)
The posted incident - and worse - will always happen, I'm afraid. Security, as well as any human endeavour, will never be perfect. Hopefully the airport security forces of the world can 'vary things up' sufficiently in order to keep the bad-actors on their toes and off the property...and out of the aircraft!