All mentioned suggestions are good but we all know if it cost too much, it wont happen.
1. Better screening at the airport including ramp worker. if Israel can, we can too.
2. Install monitoring equipment or implement a new FAA rules that require pilot to contact ground/tower at all time. if pilot fails to do so, qround take control and autopilot and land at nearest airport.
3. Better training at ground/tower. When you see a change in flight destination and no contact what so ever from the pilot, you know something is wrong. 2+2=4....