Down vote + corrective comment should do the trick.
- Downvotes alone is already doing a good job of keeping it away from the upper fold.
- A sight of a negative score is already a red light indicating a bad answer.
- Even more, a negative or corrective comment.
If the answer's owner does not take action in response to the down vote, then forever will it be given a negative remark by incoming voters and a negative reception to incoming researchers.
But sometimes, people fear losing reps in downvoting answers, so they avoid it (like I did before). Users should overcome that and use their points to improve the quality of posts.