Casting my eye over my training session notes, "DECU Hi" appears time and time again as problematic for many pilots to deal with. I see one note here where the pilot lowered the collective three times in a row in response to DECU Hi and the NR went off the dial. After being told that was the wrong thing to do, and why, and what he should have done, and then to be told we were going to repeat the exercise, and he did the same thing again. Unfortunately there just isn't enough time allocated to keep repeating the exercise until they get it right.