I have 5 kids and only ever smacked 1 of them.
Basically for months me and the wife tried everything (loss of privileges, more attention, general, discipline but never smacking him) with our youngest son aged 6 to stop him hitting his little sister aged 1.
Nothing worked. See I have never had a problem with smacking kids as a form of discipline my farther did it to me. Anyways one night me and the wife sat down and I said he needs a smacked arse if he does it again my wife agreed reluctantly. basicly he hit his little sister again. I took him upstairs gave him a smacked arse (away from everyone). Then said to him its not nice when someone bigger than you hits you how do you think your sister feels, don't do it again.
He has not hit his sister since 3 years ago this happened. If anyone ever told me that was abuse I would tell them to &*%% off. Simply put I never lost my temper and was in full control.