This can be done by making it so no one can post a link for the first 10 genuine posts, if they arnt deemed as genuine or post spam after that person is banned and post removed. But would need moderating.
Another VBulletin forum I used to be on, prevented anyone from posting for 60 seconds after a previous post. That struck me as a good idea to prevent spamming hard.
Professional bum. I post here as I have too much time on my hands :P