I had an ADF when I was a child that probably jumped out. My dad left the tank lid off just one night and that was all it took for the frog to disappear. Although we never found it, we had to assume it had escaped. This MAY have been a story to stop me being upset about my frog dying or something though

There is a small hole in the lid of my tank that I have taped up just in case, maybe I'm being too wary?

The frog will probably like to sit on objects that are by the water's surface and poke its nose out. One of my frogs in particular enjoys this, whenever I take water out to do a change he climbs straight onto the highest log and sits with his whole head out for a little while That's the closest I've come to seeing one willingly exit the water.