I have the same probelm, my grey horse comes back at me when I hit him and gets really aggressive and bucks. This is what my trainer has me do. I ask for forward eg lengthen the trot, horse gets pissy or ignores me, I hit horse he gets aggressive I hit him again until he lengthens his trot. Once we have this sorted and he is responding to the leg the attitude goes away. For me it was a matter of no you must do as your told, and once he learned that all was good.