I am trying to use .htaccess to block a specific IP from entering my site.

The code I was instructed to use works perfectly on a test IP, but does not block the offending IP:

order allow,deny
deny from xxx.xxx.xxx.xxx
allow from all

I placed this code at the top of the .htaccess file in the main catalog directory.

Any idea why the block is not working?
Do I have it in the right directory?
Should I be using a different code?

Any help would be appreciated.