Check out multi function engine monitors from EI, JPI and possibly Insight. They will do what you want and more as well. User definable limits are set for whatever engine parameters you choose. You can download the results to your PC at your leisure and send the culprit the bill for the overspeed, fiddling the hobbs, overtemp, poor warmup/shutdown etc.
Usefully, you can set a visual and audio warning lower than the POH limit to warn the pilot things are about to go wrong, so they can help prevent things like overspeeds.