As soon as you tap an aggressive horse, it is like you have broken some sacred pact. They feel they can get physical with you. Even a very gentle tap and it changes the agreement and the horse will start to follow through on its threats. You can get really big and active without touching and horses will respect this but as soon as you touch you cross a line. You see them do this to each other, they will throw heads at each other for hours but not bite, they will kick up their heels but will not land a blow. So get as loud and big as you like, but do your best not to tap them. You can block them if they are coming towards you, that’s OK. You may arrange things so that if they come towards you they bump into something on their own. This sort of thing is common with horses that get aggressive when girthing. The rider will tap them as they come around. This is where it is preferable to be ready and block rather than tap.