How can I keep my small pond from freezing in the winter?

[audioenvy]

I can't see boiling water being as effective as a de-icer and it comes with it the possibility of scalding the fish depending upon where they are in the water column when you melt the ice.

Have you thought about putting something like a long banquet table over the top to prevent snow from building up on the water and providing at least a small amount of reflective thermal insulation?

 

[MitchM]

That pond looks like a good candidate for a clear plastic cover and an air stone running for the winter.
Being next to the house foundation will give it some warmth and a clear plastic cover will protect it from the wind and allow some light to penetrate for the algae.