[Boogieman]

Anything that is going to hit us is going to take years and years to get here, and since we will be rotating around the sun all that time, nothing can really approach us from “behind the sun”. It would only be approaching us from that direction a tiny fraction of the time we would be able to try and detect it.

[dragnet2]

That's all true, however we've had asteroid and larger meteor near misses which we never detected until they had passed us or actually hit us.

In fact earth was just had an encounter by an undetected meteor which exploded over Russia, which was about the size of a school bus. The shock wave caused hundreds of injuries.