Ruining someone's reputation is not something only a government could do. Companies with enough money and a few (black-hat) SEO experts might be able to pull a large-scale reputation-kill to anyone who is an upcoming competitor or a pain-in-the-ass person. Small-scale reputation hacks happen all the time. What the heck, there is an industry where you can pump your own reputation up legally.

So the question is: how can we protect ourselves from any of these efforts (may or may not be coming from a government)?