Ban Countries!
Suggestions
here on jamroom.net when a new user signs up and they post a link somewhere to an off-site URL the whole team gets an email. "an offsite url has been detected". The URL is clipped so their post becomes:
".... Yeah, I agree, checkout this link (offsite URL clipped) ....."
So there is no gain on their part and we come along delete and ban them as soon as we get the email.
I use the WHO'S ONLINE tool in the dashboard to see if they are still online, if they are I click "Log them out" to kick them out, then delete the account and ban the IP.
Seams to work ok for here at jamroom.net.
Jamroom CMS powers this site, so you have the same features available for your site too.