There's isn't a button I can press that will somehow make someone stop posting on Law School Discussion. I can disable an account, but an account is not a person - it's just a name and a password.
In some cases, whether or not someone is a troll is a matter of opinion. Some people consider those who only post one thing all of the board to be a troll.
Problems on forums are a commen problem, and there ARE ways to remedy it. It all depends on whether or not you want to. If so, then here are a few tips:
1. Confirm email addresses when users sign up, and don't allow two users to have the same email address.
2. When a problematic user is banned, ban his IP address. If the user is behind a proxy server then just ban the first two fields of his IP (i.e. 55.555).
3. Don't allow users to delete their accounts, because it is a way around #'s 1 and 2.
4. Find dedicated and trustworthy members to moderate the sub-forums. Put one member in charge of moderating each one or two, and then provide them with a clear set of steps to deal with problematic members (i.e. warn, ban, notify admin). This way, you will not be swamped with so many problems all at once and your mods can deal with the problems effectively.
5. Implement these rules with the knowledge that it will only benefit
the forum rather than hinder it. A solid and vibrant community needs a clear set of rules so that the whole scene doesn't burst into anarchy.
Because certain members are not banned, and because certain rules are not upheld, many quality members have left either out of fear or disgust.