I personally do not like the advise to chase and spank him. Lets see I think I will lovingly run up and cuddle the the person that chases and spanks me. NOT.
Do you have a pen or area that you can work him? You usually drive them away until they face you and then you back off. The reward for facing you is you quit making them run. Lots of videos and shows like join up. I don't think you need a trainer just stick it out.
Joining up is great but if the horse persists on giving you the butt I do think they should be spanked for that. If they walk away, you turn away and stop....I do know how to do join up. But when a 1,000lb. Animal keeps turning it's butt to me I will not stand there and let that be ok....