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 a 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). It charges some fee to use their proxy blocking service.