Yes, an A/F ratio gauge is good, but it can't detect knock or do anything about it. Running rich doesn't guarantee you are safe.
If you are worried about detonation, get a system that can respond to inaudible knock and keep it inaudible.
Here is a link to a short clip that shows an individual cylinder knock controller on an engine tuned for 91 octane, but running a 50/50 mix of 89 and 91. The system is responding to inaudible knock:
bgstew6's knock controller demo
Your engines are rare and expensive. The knock controller is a small price to pay to protect it, and it won't slow you down, since it retards only the knocking cylinders.