Fab, I know you don't smack, and feel very strongly about it. So don't for one minute think I am advising it. But I thought I would tell you my story.
I used to smack my children; for quite a while, it was the only way that DD1 (who has SN) could be stopped from doing anything, and even that often didn't work. Anyway, it got to the point around Christmas time, that I had noticed that she would push, and push and push until she was given a smack. Then she would look at me and give a 'so what' kind of response (although not as sophisticated as that because she has a S&L delay). The trouble with that is, that there was nowhere else to go. I had delivered the ultimate sanction (a light tap/smack on the bottom), and I certainly wasn't going to start beating her, so what could I do next??
It got to the point where I thought deeply about my approach. I have never thought that smacking is wrong, and I still think it can be an effective form of discipline if used with measure and control (although I know most on MN would disagree). BUT - when a method doesn't work, there is no point in using it. Especially something like smacking, because you run the risk of doing it to make you feel that you are doing something about the behaviour, if you see what I mean.
So, at Christmas time, I said to DH that I thought we should completely avoid smacking at almost all costs. Instead, we decided to give "1, 2, 3" a go. To be honest, I could not see how on earth it would work. Especially as DD1 in particular (I have 3 DDs under 5) is so fixed on her own agenda.
Now, I say "DD1, I am going to count to 3, and if you don't , , , , then I am going to .
Bizarrely, the sanctions can be absolutely tiny! I often use "....I am going to help you." So, "DD1, I am going to count to 3, and if you don't get off that table, I am going to have to help you get off." I don't know why it works, I don't know how it works, but it works. The two older children scurry off of furniture at the mere mention of starting to count. DD2 (2.9) scuttles away at "One", and DD1 (4.6) who has SNs needs more time to process things, so she will often wait until I exhale after 3 and start to say 'right'
I also use the naughty step if necessary for DD2, and DD1 (who can't stay still for long enough to sit on a naughty step) gets strapped into her booster chair for 2-3 minutes to give her time to calm down and think about her behaviour.
I suppose what I am saying, is that if you get into a cycle of their behaviour esalating, and your response escalating, then it can be very hard to get out of that. You end up either going beyond what is reasonable, or running out of options.