I would expect above ground to freeze faster as well. In fact, this article uses submurged in the ground (along with some composting) to keep water warmer:
https://www.backyardchickens.com/articles/alternate-method-to-prevent-water-freezing.73180/
But, for that article, I can't figure out how...
The key is two-fold: preparation and redundancy. Have the electrical cords ready if using them. (they can be a pain to deal with when frozen.) Having multiple waters that can be interchanged throughout the day. Be ready for a plan to not work or something to fail.
There are many aquarium heater and birdbath heater types uses in these:
https://www.backyardchickens.com/articles/categories/feeders-waterers.26/
Considering that ice floats, top drinking could be a problem. I only have to water 4 hens and use a purchased ~3 gallon heater with build in...