Both yesterday and the day before my disposable diapers leaked while driving my paper route. Yesterday was bad. However, I wore a terry cloth-lined plastic pant over my diapers. The leaks were contained and my pants and car seat were saved as dry.
It's odd that two days in a row my diaper leaked, but statistics allows for that. It's notable that in over three years of using this combination not once has a leak escaped from the lined plastic pant. That's 100% security, and worth the bother.
The moral is that if you require such security, then this solution works.