Debian-Administration have made a sweet guide to use mod_rewrite to redirect unwanted users to an error page.
Enjoy the tip here.
There are several times when you'll wish to deny particular clients access to your webserver. The most common and obvious solution is to simply firewall the visitors, however this doesn't let the visitors know what went wrong. They might just believe your webserver is down. A better approach is to use mod_rewrite to redirect them to an error page.
Also, you can enjoy the new layout on their website.