How to Block Proxy?

Question: How to block proxy?

I am running a forum, I have a person who has activated app. 30 accounts, he wants to destroy our forum.
He is only using proxies, how can i block him, I know in which country he lives. I validate all new members by hand, is it possible that i check the IP using a list or program to scan if it might be a proxy?

All information is welcome, this guy is really dangerous!

Answer: There are three methods to block proxy. The first method is to check the HTTP headers. If there is HTTP_X_FORWARDED_FOR or HTTP_PROXY_CONNECTION in the headers, the visitor is using a proxy.

The second method is to make a proxy database. You can collect proxies and save them in your database. When an user visits your site, you try to find his IP from the database. If found, you can say he is using a proxy and ban his access.

The last method is to use a third-party script to block proxy access such as ($199/domain) and ($50/month). It charges some fee to use their proxy blocking service.