Keeping out the crashers

By now everyone's heard about, talked about, and probably are sick of, the party crashers at the recent White House state dinner. While that turned out to be pretty innocuous, having uninvited attendees at any event is at best going to throw off your F&B, and at worst could be a real security concern. I just read Crush Party Crashing with Tips from Security Experts from Special Events, and it has some good tips to keep this from happening to your event.