how do I prevent all images/URLs from http://spammer.com/whateverpath??

I'm sick of this guy posting messages on my bulletin board with image URL's and hyperlinks of his products for sale and he keeps using a different IP address and username, so I can't seem to stop him otherwise. Any ideas?

cPanel.net Support Ticket Number: how do I prevent all images/URLs from http://spammer.com/whateverpath??