It could be as simple as automatically posting a stickied comment to every new thread about moderation rules.

The thing is, 99 percent of threads run just fine. Maybe a poor comment here and there, but floods of them are very rare. We drop that mod reminder in maybe 1 thread a day on average, usually when it gets very popular and starts to see an influx of users who aren't regular of the subreddit so might need the reminder. There is no real need to put the reminder in every thread, and we feel it might be excessive.

Or it could be more complex – perhaps cloning threads to /r/AskHistoriansPeanutGallery and directing incorrect, speculative, or otherwise disallowed comments there.

The idea of some sort of META discussion subreddit has been floated in the past, but we aren't interested. While it would mean a relaxation of some rules to allow wider discussion on a given topic, we would still need to monitor it to ensure that discussion remained polite and reflected what the /r/AskHistorians community is about. As such, it would require considerably more work from the mod team.