I understand that bolides would be the biggest danger right now, as they are small enough to be practically undetectable, but may be large enough to level a city. Are there any measures we can take against them? [0]

[0] I'm aware one of our best bets here would be a proper survey and sensitive enough telescopes/satellites actively looking for these kind of objects. And that there are some projects and programs along these lines already. It'd seem there's some more work to be done in that area though.