Anonymous wrote:OP here -- husband agrees with me BUT is petrified of his dad (probably because of the "swattings" from when he was a kid!). So is unable to comprehend saying "no" to his dad.
All the more reason to say NO.
I am a pretty laid back parent and there are many areas where I let the grandparents make decisions when they are watching the kids - amount of TV, sweets, bedtime, etc. However I will not compromise in areas of physical and emotional safety. To me spanking is firmly in the non-negotiable category. If you can't promise not to spank my kid, then you don't get to watch them, full stop.
Just be polite but firm that this is a deal breaker. And while I'm normally in the camp that each parent deals with their own side of the family, I think in a case like this it might be easier for you to be the one communicating this, since it may be easier for you to stay firm by unemotional since you don't have emotional baggage from childhood with this person.