Fretting about detection avoids the obvious dilemma: knowing about a problem and solving it are two very different things.
As far as detecting rogue celestial objects, the answer might lie with a single devise, a powerful, wide angle laser. In a way, acting like a spotlight, used to illuminate enemy aircraft at night in WWII.
Right now we know that if you shine a 3.5m wide laser at the Moon, through Earth’s atmosphere, when it hits the moon, it will be over about a 2km area, at 90% strength. We know this because it is done right now at the Apache Point Observatory laser-ranging program in southern New Mexico.
Granted, objects that threaten Earth are much further away, but would become glaringly obvious with even faint illumination. And since most threatening objects come from only a single sector of space, the asteroid belt, it strongly reduces the amount of space we need to search.
But what do we do about it? That may depend on the threat. If it is small enough, we might just blow it into pieces too small to do much harm.
Larger than that, we can use distance to our advantage with deflection, using some technique to deviate its path by a tiny amount that will be multiplied over distance to miss the Earth entirely.
And for the really large threats, we might attach engines to smaller bodies, and put them on a collision course with the threat body.
In any case, this will involve prepositioning drone spacecraft in deep space.
True. Then we should do it and charge the rest of the world for the protection.
Such would be roundly attacked, with the Socialist nations contending that we were only going to use the incoming masses as weapons of mass destruction (pardon the pun).
I have long maintained that the high ground of space is a strategic asset, and that whomever occupies it would only have to throw rocks.