Get dogs trained to detect explosives patrolling all areas of the airport and I'm not sure what they're called, but they have these sniffer devices at the CN tower where they basically make you walk through a large hairdryer and it sniffs the residue blown off you for chemical signatures. It's not perfect, but a combination of those two things any place where you have large volumes of people congregating would surely yield an above average result. The dogs alone I would wager would be an efficient response - they're portable, don't take up much room and can clamber over all kinds of obstacles.