It isn't possible to block a whole country, individual, or anyone at all because of proxy services like razorproxy . com However if you must try there are a few services out there that compile and change the lists for you. You just set up a daily download and your file uploads every day. Haven't used these services for awhile but they should still exist.
I use a site called Traffic Cleaner (just google it, or add .com to the end). It's pretty good, you just insert abit of code into your site entry pages, and the above site filters out any undesired countries or specific IPs. It also has a white list to allow specific IPs.
Started off free, but I now pay a monthly fee for a more premium version.