Stephen, I'm probably not the one to be givin advice, I'm still learnin.
I picture your fountain as a floating or barely submersed sprayer. I would think that would freeze up during the cold. If you're sharp enough to fabricate something like that I'd think you could put together a DIY aerator fairly inexpensively. Do a google of DIY aeration/pondboss. There are also summer kill offs that I'm not qualified to explain but I just run my aerator for 4-5 hrs pre dawn everyday. Don't know if a fountain would provide proper protection.
The winter kill problem is usually caused by snow depriving the water of sunlight. without sunlight the plants and planktons die off. As they do they absorb the oxygen out of the water thus suffocating the fish. I only turn a shallow aerator when the pond has had snow cover of 3 or more inches for 7-8 days. I leave it run till there is about an 18-20' opening. That is probably being overly cautious but it took awhile ta grow the fish to a good size and I don't like gambling.
My personal opinion is that aeration is one of the most important things I've done to make my pond healthy.

Do nature a favor, spay/neuter your pets and any weird friends or relatives.