This is somewhat similar to ModSecurity but in PHP, and thus configurable via Tiki.
"PHPIDS (PHP-Intrusion Detection System) is a simple to use, well structured, fast and state-of-the-art security layer for your PHP based web application. The IDS neither strips, sanitizes nor filters any malicious input, it simply recognizes when an attacker tries to break your site and reacts in exactly the way you want it to. Based on a set of approved and heavily tested filter rules any attack is given a numerical impact rating which makes it easy to decide what kind of action should follow the hacking attempt. This could range from simple logging to sending out an emergency mail to the development team, displaying a warning message for the attacker or even ending the user’s session.
PHPIDS enables you to see who’s attacking your site and how and all without the tedious trawling of logfiles or searching hacker forums for your domain. Last but not least it’s licensed under the LGPL!"