Guess I wasn't hard core as I never heard of putting warm water on lake or pond ice. We had a pond real close to our house and someone with a jeep would plow it off for us kids. It was behind the library, so there was a street light and we'd skate until suppertime. I had swollen knees from hitting cracks in the ice, all winter. My general helper showed me her knees from skating a lot, looked just like mine 60 years ago...
My kids both played hockey. We actually did a back yeard rink one year when we were living in town. My dad even built a nice net. Well... he overdid it a bit. He used 2 inch steel pipe and the thing weighed a ton. Easy to slide around on the ice but really hard to move otherwise 😅