I am still too much of a rookie to be trusted with a crop, but last fall I took a few lessons (Western) and was told to smack the horse's shoulder with the free end of the reins when he became stubborn. I did it twice, but it felt wrong to me. I decided my instructor was teaching me to be a more aggressive rider than I really wanted to be and switched lesson barns. When the mare I ride now refuses to do something, it's almost always because I haven't asked correctly, or I confused her earlier and her patience with me is at an end. Of course, I'm not suggesting this last is true in your case - if you're galloping, you're certainly WAY more advanced than I am! - but realizing my own ineptitude has made me really happy that I refused to continue to strike my former horse teacher.