I've never used corporal punishment, and I never will. Our worst case punishment is time-out (1 minute per year old). I still remember hearing about her reaction from her grandmother. The sheer horror on her face, when she discovered that nanny knew about time-outs!

Even timeouts generally aren't needed. It's been over half her lifetime since we last used it. Her respect and love for us is more than enough to enforce good behaviour. We actually have to be careful, the smallest bit of upset from us creates a disproportionate reaction in her. Knowing she's disappointed mummy or daddy hurts her more than any amount of beating with fists (open or closed) could achieve.

Just to add.

If people do advocate (even jokingly) for spanking, I take it seriously. I point out I am using the best scientific knowledge we currently have, to achieve the best results for her. If they don't immediately back down, with their tail between their legs, I point them at something like this :

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3447048/

I do try and be kind with the older generations however. They didn't know better, and often we're doing the best they could. That's no excuse for not adapting their advice to the times however.