In the past I've trolled reddit subreddits by spamming shit and getting them to place restrictions on new accounts. It is a counter productive approach. You give the troll what they want which is to cause chaos and make it harder for people to have a discussion. And the troll can very easily just get around it by pretending to be legit long enough to get in the door than shitting everywhere.

The best way to handle the troll is just to ignore them. Block them if you wish but it doesn't matter since they make new accounts. Just ignore. Troll will eventually get bored. Not much else you can do to stop it unless you want to break the message board format or move to something a lot less anonymous