At that age, a firm "no" seemed to work for my DD but now that she's a bit older (22mths) I am finding I need to use "consequences" for her instead and that REALLY seems to work!! I give a warning first..... ie "if you do that again, I will have to take away your necklace and you won't see it until tomorrow" (she understands VERY well!!) and she will immediately stop what she was doing and say "nooooo" and grab her necklace tight
if she continues to ignore me, I follow through with what I said (always follow through).

I think every child is different and what works for them last month may not work as well this week...kwim? Good luck. HTH

And don't worry about what other parents are doing with their kids....you know your DS and what works best for him.....if that means giving him a gentle smack on the hand (depending on what it was for) then so be it. If that works, then great. I've had to give my DD a gentle smack on the hand once for doing something very wrong (which I felt so bad about ) but she just laughed at me so i haven't done it since.