I constantly look under the vehicles for leaks. None have been present - so I've grown accustomed to checking the oldest vehicle every three weeks (approx 700 miles). With 170K on the odometer, I usually find it a half-quart low.
The rest of my vehicles are younger & driven less miles, but since I'm already outside checking the oldest one, I raise the hood on the other vehicles too. Usually, all that's needed there is a refill of windshield washer fluid.