I have to agree.....in five years, we've had one eel climb out (a ribbon eel that had done fine for over a year in one uncovered tank, but left his new home within two days of being put in the new, deeper tank)
It's been our experience that if they are in a roomy enough tank with plenty of food (very good point made there, by the way) they are more than content to "stay home".
We currently have a SFE (6 years old and huge), an occelated morey (going on his 2nd year...about 27") and a green wolf eel (not a true eel, but try to convince visitors of that) that's 18" plus.
The single most important factors seem to be sufficient food and plenty of LR.......if underfed or in a relatively bare tank, the liklihood of the eel leaving is astronomically high, even with a good cover (in a shallow tank where they can get leverage, they are surprisingly strong and capable of lifting more than many imagine)