A list of known proxy's can be googled.. Block those IP's by default...
Forget about those dial-up webmasters.. Also block all known dialup IP's.
Use a new approval procedure, where webmasters need to fax a copy of their ID before a link is added..
MD5 Hash the user's screen resolution, color depth, browser plugins, user agent and ISP's name and use that as lead indicator for multiple submissions.
Or just relaxed and monitor your database now and than..
