I've been practicing at a local lake that has thousands of ducks on it every day (it isn't huntable) listening to the hens then trying to repeat. In my mind real ducks are better than any video, tape, teacher you could find.
Good luck, we all need it 

Nature is your best cure.
Also, feed back is crucial... you are right that having someone tell you what you did wrong will make you better.
But.... if you record yourself, and listen back to it, you can hear it better. Maybe something that simple will make you HEAR what you are doing wrong, or right.