This year will be the test on the fountain and its fish. I was told that goldfish can survive almost any freeze. I turned off the fountain and let the pond freeze this year and wasn't too diligent about chopping a air hole. Hopefully there will be enough air pockets between the ice and lower water line.
It is amazing to watch the fish - perfectly still in the cold water. Makes me think about my own winter lethargy and hibernation. It's tough to get out of bed on a cold Saturday morning.
There are plenty of pockets of air between the covers and the mattress.