That's a very good point I hadn't considered.

I wonder if Dumbledore has actually done any experimenting over the last 50 years, like the one-year contracts I suggest downthread, or having two staff members rotate responsibility each year (and teach something innocuous like Muggle Studies in the meantime).

A also wonder what kind of curse would have such an incredibly powerful effect, and whether Voldemort could have used a scaled-down version of it to, say, get Dumbledore out of the headmaster position. Bearing in mind the original curse was cast before Voldemort had even achieved his full power.