On a forum I manage I ended up implementing a a stealth moderation queue for new posters. Basically their posts don't show up for anyone except mods and themselves. So they think the post went through and move on. A mod can then approve or deny the post. When they approve it removes the stealth moderation flag for their account, if denied, it deletes all posts and the account.
I also had a spam filter at one point, it worked kinda like an email spam filter where certain keywords gave a certain amount of points and if you went over a certain amount it just auto deleted the post and the account. It would only activate for new accounts and like the first 5 posts. Somebody who knows about it could theoretically get around it though but it worked 99% of the time.