One of the problems, as I understand it, is that some of the debris gets captured by our sun’s gravity and creates a “long period” comet. The comet then goes way out to the Ort cloud and , many years later, returns. The fact that it keeps making passes ups the chances of getting hit.
A good read is: https://www.amazon.com/Cosmic-Serpent-Victor-Clube/dp/0876633793/ref=sr_1_4?s=books&ie=UTF8&qid=1490282825&sr=1-4&keywords=the+cosmic+serpent
Interesting. Could we not intercept material by going outside the ort cloud? Viking is out there already, is it not?