Fitting indicators to your vehicles wheels is a good way of ensuring wheel nuts are locating correcting and are tight.
If however, you do not have indicators fitted or you require additional assurance, a Wheel nut torque log is a good idea.
Issue your fleet with a torque wrench set to the correct figure and show your drivers how to use it. The findings should then be noted in a log to demonstrate regular checks are being made.
Checks should then be made on a regular basis.