2) Give people guidelines about what is acceptable, with #1 being "don't be an !@#$%^&" (or something similar). (No, that doesn't mean a set of ironclad rules that can be lawyered and gamed. It means guidelines.)
I would add that when these guidelines are broken, any action taken is noted publicly (with the offender remaining anonymous, if possible). My initial thought would be to add a final post whenever a thread is locked explaining why it was locked. Leaving warning signs lying about leaves clear indicators that certain behaviors are not allowed instead of leaving people in the dark about what happened.
For other actions, I'd just use that case as a specific thing to add to the guidelines. For example, let's say I am clearly posting only flame responses, but I'm not limited to one thread; make a specific note under "don't be an !@#$%^&" saying, "Flaming is not tolerated." etc.
