Under saddle, same thing , forward movement, set my hands, they'll bump themselves. Of course some of our trails are narrow and there is a smorgashborg of delicious leaves! Let's say T moves her head to the right to snatch some leaves, all I do is set the left rein, and move her forward. She learnt quick that not only did she not get her snack, she had to move out a bit more! Being a horse who likes to conserve her energy,haha, she was a fast learner.
Walka, never allowed him the opportunity to develop these habits, so haven't had to deal with it with him.