Since everyone here likes talking about the problems with airport / airplane security at various airports (of which there are plenty of examples), how would you design airport / airplane security if you had a free hand to do it from scratch in order to offer security at the desired level without excessive inconvenience to passengers? Questions to consider:

What threats are you concerned about, and what level of security against such threats is desired?

What is allowed or not allowed in the cabin? In the hold?

When are passengers and baggage checked? (i.e. do you have a large "secure" area, or do you have security screening at the gate, or some other place?)

How are passengers and baggage checked?

What background checks on passengers, if any, would be used? What would be done if a background check indicates that a passenger is a threat? How are false positives handled?

What security features would be designed into airports / airplanes? (e.g. armored cockpit doors, or decoys against heat seeking missiles)