Within your <Directory> Tag,
either allow certain ip's to access your site, or deny certain ip's.
the best way is to:
Deny from All
Allow from ....
Simply replace the "..." with the IP's that you wish to allow access to your site. You may also implement this using .htaccess
It's always best to deny everyone from accessing your site, and then allowing the select IP's that you trust to view your site. However if you know of the exact IP that you wish to block and not block everyone else, do the reverse:
Allow from all
Deny from ...
replace the ... with the IP's you wish to block separated by spaces or add a new "Deny from ..." for each IP you want to block