There are plenty of automated tools out there that can filter content. If you allow visitors to your web site to add comments, then you will need to filter them. This insures that people use wholesome language. But how do you keep the SPAM solicitations out? Well, there are tools available for that also. They will check each link to see if it matches up to a known SPAM site. If it does, or the language is inappropriate, then the tools will flag the comment as needing review. Or you can optionally just delete it. Either way, let the tools take care of the headache of trying to keep comments appropriate.