Any 2-1, 2-2, 3-1, 3-2, 3-3 where the defenders have to communicate to identify the situation and who each is covering would be good. Also play full ice and have the farthest player from the puck stretch and the D has to learn to scan the ice and honour the stretch man instead of focusing on the puck. You could vary the stretch man also so it isn't predictable.
The basic principle is that no one can get behind them and only one player go with the stretch man, not two or more which happens a lot.
'The Game is the Greatest Coach'
'Enjoy the Game'