I would smack him if he is behaving inappropriately too close to you. Although I don't smack on the top of the croup, I try to aim a smack on the rear to the side of the tail, like spanking a naughty child. It teaches them that there is a zone around you that expects proper behavior. Last summer, while bathing a mother and her 10 day old filly, I disciplined (smacked the butt) of the filly when she was kicking her dam within arm reach of where I was standing (spraying the water that was cold and upsetting her a bit). She jumped away and then went to the far side of her dam from where I was to continue kicking her mom. Although she never once even thought of kicking at a person, she learned with one simple smack on her buttocks that kicking in a person's vicinity was unacceptable. Babies learn fast, they want to please the boss and play hard with those that let them.