Taking LAX for an example... It has a perimeter of 4ish miles. Assume one sentry with a shotgun, loaded with birdshot every 300ft to give decent coverage of the

Taking LAX for an example... It has a perimeter of 4ish miles. Assume one sentry with a shotgun, loaded with birdshot every 300ft to give decent coverage of the perimeter, that gives us about 60 sentries. At 15 $/hr, 24/7, that gives a minimum cost of about $7M/year, ignoring any overhead for management, training, firearms, secure storage, etc. All that achieves is to secure the airport, poorly, against a very unlikely threat, and one that is unlikely to down a plane even if an intrusion occurs.