[CentOS] Apache Changing IPtables C 5.6 via Apache

> When a web site is attacked, so far by unsuccessful hackers, my error
> routine adds the attackers IP address, prefixed by 'deny', to that web
> site's .htaccess file. It works and the attacker, on second and
> subsequent attacks, gets a 403 error response.

Have you looked at mod_evasive? 
http://www.zdziarski.com/blog/?page_id=442

Barry