One of the most effective way to catch spammers is to allow them to fill in their homepage. Spammers almost always fill in the home page field if you give them the opportunity. Then if its filled in then moderate the account.
There are 3 urls that would need to be ignored for this feature because members tend to fill this in:
google.com
facebook.com
yourdomain.com
There are 3 urls that would need to be ignored for this feature because members tend to fill this in:
google.com
facebook.com
yourdomain.com