how to stop spammers without using replacement variables

[amcd]

On our board we get quite a few spammers trying to drive traffic to their own site. We usually ban them or edit their posts to stop them but sometimes we get persistent characters who keep registering new ids from different ip addresses. In such cases we use replacement variables to change their site's url and that certainly discourages them immediately.

But the problem is that the list of replacement variables is getting quite long and I think it must be slowing down our server as well. Is there any way to achieve this objective without using replacement variables?

I saw a suggestion that we could add smilies with the offending domain name as the smiliy shortcut. That hides the url from view, but still leaves the url as a clickable link, and the url is visible by clicking 'quote'.