Here, take a look at this from Sherdog and how they run it:
http://www.sherdog.net/forums/f2/sherdog-user-rules-faq-contact-info-all-new-members-read-17836/
Full transcript:
Welcome! Sherdog is a private forum so posting is a privilege, not a right. All rules are subjective to administrative interpretation.
***Platinum Members Please Note*** -- While we greatly appreciate your subscription and support, these rules apply uniformly to everyone, with no added leniency given for paying members. If you commit a ban infraction, your money will be lost rather than pro-rated or refunded.
Double Yellows: last 30 days. Members lose many posting abilities. Any infractions while carded = ban.
Double Yellow Infractions
1. Fighter Bashing (including refs, promoters and the like) won't be tolerated. Criticism is fine, flaming, steroid allegations, etc. isn't. Minor bashing such as "so and so sucks, is a can, etc." is a double yellow, while extreme bashing like "so and so is a pile of shit, bitch, ***got, etc." will result in a ban.
2. Postwhoring. Posting "+1," "too long, didn't read," "rickson by armbar," empty quoting, cool story bro, pic-whoring etc., will result in a double yellow card and post count reduction. If it's a number of posts, you will be banned for trolling.
3. Scrollbombs, gigantic pictures that disrupt threads, or posts designed to cause thread or computer problems. Quoting scrollbombs, infractions or problem, empty posts.
4. Posting video clips of events recently shown on pay per view. Posting full fight clips from unauthorized copyrighted events. Includes outwardly soliciting/providing via pm.
5. Nudity. No bareass, assfloss, nipples or graphic poses, avatars included.
6. Copyright infringement. Ex: If a site posts and interview, post a link don't cut and paste the entire article.
7. Profanity in the thread titles.
8. Knowingly or repeatedly posting material in the wrong forum; if you are unsure, feel free to pm a moderator.
Ban Infractions
1. Hateful Comments. "Shut up ***," "Fuck you Newb," etc.,
2. Member Harrassment (including pms, threats).
3. Tape trading/selling.
4. Using an alternate account while carded.
5. Orchestrating forum raids.
6. Posting a private conversation or personal information without consent.
7. Trolling (posting ridiculous/non-sensical/irrelevent/racial/disturbing comments, images or links), spamming, posting to stir shit/cause problems.
8. Porn. Posting, quoting or outwardly soliciting/providing pornographic images or links, empty posting, lol-ing and t-ing porn posts or threads. *See Off-Topic Sticky for more specifics regarding posting outside the fight forums.
9. Posting fight spoilers outside the spoiler forum (shows on tape delay in the U.S.). Requesting/Providing Illegal streams.
***NOTE*** -- We're only interested in what happens regarding the website; if your brother, ex-girlfriend, drunken asshole buddy, cat, gets into your account or starts posting infractions while you're on the toilet, the account will take the bullet regardless.
If you see a thread getting out of hand please pm a moderator and it will be taken care of.
I think the "Double Yellow" concept is a cool idea.