OK, I see now. I got confused as I heard that it took only two years to recover the money - but that is for TeamJQ etc.
It is called environmental conditioning. You make the conditions and work environment such that your workers stay long enough to recover the cost of their training and then leave at their own accord.
A few years ago (2003?), Aer Lingus was the subject of leaked documents detailing the environmental conditioning required to have their cabin crew leave at their own accord.