All it takes is 7 simple lines of code in the .htaccess file in your site's root. Here they are:
<IfModule mod_geoip.c>
GeoIPEnable On
Order deny,allow
deny from all
SetEnvIf GEOIP_COUNTRY_CODE US TargetLocation
Allow from env=TargetLocation
</IfModule>
You must of course, first install Maxminds GeoIP api on your server. Download for free here: http://www.maxmind.com/download/geoip/api/c/
Then install the Apache module mod_geoip. Download for free here: http://www.maxmind.com/download/geoip/api/mod_geoip2/
Then add those lines to the .htaccess file
Done. All http requests from outside the US will be denied. If you are on a shared server, forget it. You need a VPS or dedicated to do this. Being able to install whatever you want on your server is a wonderful thing. It took about 10 minutes to install this on CentOS (No yum install, and I did have to instal zlib-devel [yum install zlib-devel] as a prerequisite).
