Guest books have increasingly become a target of Internet spammers because they are so easy to find and exploit. There are a couple of things you can do though to discourage them. The first option is to use a moderated guest book where you get to review each entry before it is posted. However, this can be very time consuming if you have many guest book entries everyday.
Since most spammers use robots to locate your page, I would suggest making it harder for them to find you and thus reduce or emiliminate such spam. One way to do this is by periodically moving the location of your guesbook so that the URL for it is different. That way a robot will not find your guest book if you move it up on folder or rename it. I prefer to modify my HTML code. Just place "NO index tbd" in the head of your HTML or place it in robots.txt with instructions not to spider your guestbook. This will make impossible for spammers to find your guestbook because it will never appear in search engines, and no robot will be able to find it using this simple addition to your guestbook.
I hope the above is helpful.
Peter
