Good on him. I see tons of kids who could use a slap in the face. Unfortunately, had many of these parents slapped a hand or a butt when the kids were smaller elevating to a face slap would probably not be necessary.
I've never had to discipline my kids like that but they got a good number of spankings. Now I just use "that voice" that can scare the bejesus out of 'em!"
My wife on the other hand is a screamer, as was her mother. It got to the point that Annie would be really mouthing off to her (~13 to 14) and I'd tell Cindy to slap her in the mouth. Cindy couldn't bring herself to do it and I'd have to step in and warn Annie not to talk to her mother like that.
Thankfully, it's gotta be almost 5 or 6 years that either of them were spanked. It's good to teach them when their young (IMO).
Brian