Re: Noise association
Yeah I dont think the noise will work, you really need to work on your body language and assertiveness, its not easy if your not used to it but it is amazing what a difference it makes. Also Nix's idea is a good one, if Coco ever got nippy I squared my shoulders and pinched his neck as if I was biting him back, it was quick and there was no shouting and no further outcomes but if I was the top horse in the field he wouldn't dream of biting me and if he did he'd get a bite (if not a kick) back so that is the appraoch I took! If he is just mouthy and trying to nuzzle and nibble at you just continually push his head out of your space and also agree with TommyTank back him up a step or two, he has to learn to respect your space and the only way to explain to him what you want is to consistently push him out of your space when he gets too close and crowds you.
Re the body language might sound stupid but try it in the mirror or on a friend to get it right, if you walk towards him with your shoulders square, head up high and with meaning and believe that if he doesn't move out of your way you will walk straight through him, if he still doesn't move as you get close, use your arms to forcefully push the air just in front of him and if he still hasn't moved by the time you get to him use the tips of your fingers your fingers to firmly push him back and do not accept no for an answer. As soon as he moves remove the pressure, relax your shoulders and tell him he's a good boy, then repeat, square up and mean it and make him move away from you. It takes a while initially but once they click and understand what you want they will learn very quickly and very soon you wont even need to touch him just a wave of your arm or pushing the air in front of his chest will get him moving for you. If he tries to turn or spin, give him a firm snap on the lead rein to let him know you are still there, you still have him and the session is not over until you decide it is over. He has got to learn to listen to you and if he is not hearing you or choosing not to hear you you need to make your body language louder as that is what horses respond to. There is absolutely no way a human can outpower a horse even a tiny one so your body language has to be stonger, its all in the power of the mind not physical force.
Good luck and dont give up, we have all been there at one time or another with a dominant horse or one that has just never been taught what is expected, the 1st bit of getting him to listen is the hardest bit once he catches on and realises you wont take no for an answer and there is no point arguing they tend to improve very quickly. Juyst remember everytime he does as you ask, even if its only small, release the pressure and give him a reward instantly even if it is just a 'good boy' as he will learn quicker when he gets postive reinforcement for doing the right thing.