An effective way of dealing with spammers is letting the community moderate it. You can add a "Mark as spam" link to every post and only make it visible to users with a certain amount of karma or whatever metric. Basically giving trusted members the option to moderate.

On top of that, record the IP address of the poster, and display the post but only to the spammer. Basically hiding it from everybody else. The spammer will think the post is still active. Everybody else will not see it.