I have to agree with AAAAA untill you and hubby are singing from the same hymn sheet you are fighting a losing battle.

Next I would pick on one thing just the one and say NO and mean it, ie no hitting at all, have a chair ready for him to sit on when he hits anyone at anytime not matter what you are doing stop and sit him on the chair hold him on it if you have to.

He should be made to sit on the chair for one minute for each of his young years in his case four minutes. Then he can get off. If he is in a situation when he would normaly hit and he dosent then have some penny sweets ready and give him one sweet saying in a loud over the top voice about how good he was and isnt he a great boy ! etc.

Ignore as much as you can any other bad behaviour just pick on the one thing for now and when he gets the point move on to somthing else but keeping up with the no hitting one, gradualy add things on, but its so very important to get hubby on the same side as you or he will just learn to play one of you off on the other.