There is just one solution to this frequent problem: get yourself a plane.
Then you log total moving time (brakes off to brakes on) in your personal logbook.
You log the
airborne time in the aircraft logbook(s). All time-based aircraft maintenance is (or should be) based on airborne time only.
The above is correct for both G-reg and N-reg ops.
Anything else (like taking the reading from some meter in the dash) is mandated by the fact that a lot of people (both students and instructors) cannot be trusted to report the correct times
Charging for BO-BO (common in many schools) encourages crazy behaviour on the ground, but the reality is that if they charged for airborne time only, the hourly rate would have to go up to compensate for the reduced income.