Guardog is a simple but powerful intrusion detection system (IDS) that works by inspecting messages from log files, network packets, and other sources. It uses Perl regular expressions to check for any bad messages.
You can download it from the following link: https://packetstormsecurity.com/files/download/98110/Guardog-0.91.tar.gz
Source: https://packetstormsecurity.com/files/98110/Guardog-Intrusion-Detection-System-0.91.html