grr. spammers

I maintain a webpage for a feminist women/lesbian project. It's not like the site is insanely popular or anything. That site also has a guestbook. Now, there are some more or less normal entries, then lots of spam, that has to be deleted. Though I have no idea why anyone would want to advertise sites selling cheap viagra and online casinos in that guestbook in the first place, but whatever. So I disabled the function to post linked URLs, etc., anything that might make it attractive to morons, and check the guestbook regularly to delete the spam. But really, someone advertising his website for some agency to find men "Brazilian women" (from the wording it sounded a lot like trafficking if it was indeed real, or some porn site if it wasn't) -- WTF? I mean it is a really simple guestbook script, it doesn't even log IP addresses, nor does it have the option to block certain IPs, but if this barrage of spam that is increasingly disgusting doesn't let up, I either need to disable the guestbook completely, or install a more sophisticated script, offering more options to deal with this dren.