we thank you for your post but I'm afraid that there has been very little feedback regarding TACACS and TACACS+, it is unlikely that we'll ever develop a sensor for this niche/protocol. Alternatively, you may consider writing a custom sensor via script or exe and integrating the sensor with PRTG.
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.