Spam continues in guestbook

Hi all. I have spent the last 3 days having my guestbook spammed constantly. i have deleted all of the messages bar one which the name is "Sem-Handylogos".

I have tried all of the fixes I could find but nothing seems to stop the bots coming back for more.

Can someone help?

This is my guestbook..

http://www.live2bmx.co.uk/book.html

the spam bot called "Sem-Handylogos" is on page 2 (unless more bots have spammed the book to death by the time someone reads this)

In the Advanced Guestbook forum, th eone dedicated to Advanced guestbook questions, the first thread is called Adding a simple human verification test.