Do as much homework as possible on anybody you allow to interact with your horse. Do as much preparation as possible before you allow somebody to work with your horse.
I am a huge fan of teaching a horse to follow the feel of the inside rein and offer a lateral bend through its whole body. One of my most regular Ross-isms at clinics is “The bend is your friend.”
Why do so many serious dressage riders I know dare not take their horse on a trail? Is it because those horses do not have the makeup to be safe on a trail?
Problems with a horse are not fixed because we want them fixed it. For things to change with our horse it must begin with things changing with how we work with our horse.