The Sentinel

In one of the behind-the-scenes featurettes for the film, a Secret Service consultant to the production stated that actress Eva Longoria far surpassed the other actors in "shooting school". In fact, he remarked that her score would beat about 90% of members of the Secret Service. Longoria mentioned that when she was younger she often accompanied her father to the gun range, so being around and handling guns wasn't new to her.

The meaning of the password "CRYSTAL" was "follow my orders".

As screenwriter George Nolfi honed the screenplay, producers Marcy Drogin and Michael Douglas brought in Clark Johnson to direct. Johnson had previously directed a pilot for a series about the Secret Service called Secret Service (1992) [See episode: Secret Service: The Stalker/Bomb Protective Mission (1992)] which pointed to his interest in the topic. Johnson, also a respected actor, had worked in almost every area of the film business, including stunts, special effects, and camera. In addition, he was experienced with law enforcement action thrillers, ensemble pieces, multiple cameras, large set-ups and special effects. For The Sentinel (2006), Johnson used this extensive background to depict the reality and grittiness of the Secret Service world.

Actor Kiefer Sutherland responded with equal enthusiasm about co-star and actor-producer Michael Douglas as the latter had said of him: "If you look at Michael's films, they're Class A. I had the pleasure of working with him when I was very young, and he was so gracious and kind to me. I watched his films over the years and learned what makes him a phenomenal producer. There's a sense of responsibility and dignity in all his films. I've watched his table-read, his notes, how he handles himself on set. It's been an education and a pleasure, and I'm grateful for that."

All of the film's principal three stars who play USSS (US Secret Service agents) - Michael Douglas, Kiefer Sutherland, and Eva Longoria - gained new respect for what USSS agents do. It's difficult to run, move and shoot at the same time. Armorer & weapons specialist Charles Taylor said: "Our stars have that cool and confident look. They all exude it. But women are generally better shooters. They're more still. They don't have all that testosterone coursing through them. They just look through the sight and not at the target and they hit it."