Do you mean block people from accessing your website via proxy? Well, it's not perfect, but there is a way to do something like it. Just add the following to your .htaccess file (or create it if it doesn't exist):
Code:
RewriteEngine on
RewriteBase /
RewriteCond %{HTTP:VIA} !^$ [OR]
RewriteCond %{HTTP:FORWARDED} !^$ [OR]
RewriteCond %{HTTP:USERAGENT_VIA} !^$ [OR]
RewriteCond %{HTTP:X_FORWARDED_FOR} !^$ [OR]
RewriteCond %{HTTP:PROXY_CONNECTION} !^$ [OR]
RewriteCond %{HTTP:XPROXY_CONNECTION} !^$ [OR]
RewriteCond %{HTTP:XROXY_CONNECTION} !^$ [OR]
RewriteCond %{HTTP:X-FORWARDED-FOR} !^$ [OR]
RewriteCond %{HTTP:FORWARDED-FOR} !^$ [OR]
RewriteCond %{HTTP:X-FORWARDED} !^$ [OR]
RewriteCond %{HTTP:HTTP_PC_REMOTE_ADDR} !^$ [OR]
RewriteCond %{HTTP:HTTP_CLIENT_IP} !^$
RewriteRule ^(.*)$ - [F]
That should take care of most of them. ;)