I asked a question on Christianity Stack a year ago and chose an answer as being the best. A new contributor has now recently posted four different answers, some of which do not even address the question. I've already asked them to select one answer and delete the rest, but to no avail. More answers keep turning up! Can the community protect my answer to prevent this unwanted attention?
If someone is posting bad answers, downvote and they'll eventually find themselves answer banned.
If they're posting non-answers flag 'em and mod's will have to deal on a case-by-case basis. If it's harassment, then expect them to be booted (for a time) from the site immediately. If they persistently offer non-answers after being asked to stop then they'll probably be booted as well.
Caleb explained a case where just downvoting is not a great idea because it often makes it harder for mods to find, but I can't recall the reasoning behind it, hopefully he chimes in as well.