> check every trash can for a bomb at every big event? Actually, I think they already do that, with bomb-sniffing dogs. But they have dubious reliability, and

> check every trash can for a bomb at every big event? Actually, I think they already do that, with bomb-sniffing dogs. But they have dubious reliability, and don't catch someone who's willing to place the bomb shortly before it detonates, as may have been the case here.