Author: Bob Ray Bob's Guides
Documentation: LogPageNotFound Docs
Bugs and requests: LogPageNotFound Issues
LogPageNotFound is fully compatible with MODX 3
Questions about using LogPageNotFound MODX Forums
LogPageNotFound is a plugin for MODX Revolution that logs all requests that result in a page not found (404) event. LogPageNotFound is useful for identifying links, both inside your site and elsewhere, that don't take the visitor where they expect to go. It is also useful for seeing the activity of miscreants looking for security vulnerabilities.
Using the log, you can create rules in .htaccess to direct users to the page they are looking for and block would-be evildoers.
The plugin will not slow down your site at all, because it only executes when a page is not found.