Down vote + corrective comment should do the trick. If the answer's owner does not take action in response to the downvote, then forever will it be given a negative remark by incoming users. A sight of a -1 already is a red light, even more a negative comment or a correction comment.
However, "drive-bys" are another problem, both in questions as well as in answers. As you can see that the user is anonymous and only has 1 rep point. I saw this answer once in StackOverflow where it was accepted, but was severely downvoted to the point that it was "greyed". We should do some general cleaning of these types of users and answers.