Every Tuesday and Thursday morning, I'm coaching my boys early in the morning. They all have uniquely different styles of freestyle with varying strengths and weaknesses. One in particular, Jonas, was having difficulty with over rotation in his freestyle.
I tried getting him on a snorkel, and focusing on his head position that way, and it worked fine, until he took off the snorkel.
With him swimming and me walking alongside the deck, I would look down and his arms would cross over quite dramatically as he overrotated, and also took a breath almost at his 12 'o clock rather than a 4 or 8 o'clock position.
He has been playing a superhero game on the ipod where Superman blows his enemies away with his laser vision. I explained that he should imagine he is superman when he swims and intensely focuses his vision on the bottom of the pool directly beneath him. And by so doing, creates a laser between his eyes and the pool bottom. If he crosses his hand or arm in front of that line, his arms/hand will get cut off at that point.
Once I added that imagery to his mind, he then started having a high elbow pull, his back almost remained flat in the water, with his hands pointed down towards the bottom of the pool and palms facing behind him. He no longer had the cross over and it also fixed his over-rotation! It was like a totally different swimmer just jumped in! Now that we have that imagery that corrects the problem, we gotta keep working on that and get the muscle memory to kick in.