Run the inflow pipe below the frost line so it doesn't freeze. Bring it into the pond below where the pond will freeze. Make a 90° up, and drill a 1/4" hole in the elbow. Bring the pipe up above the pond surface and figure out how you want to end it to add O2. During the winter, move your shallow wintertime aeration diffuser close to where the water enters the pond to keep that area ice free. Drilling the hole allows the water to flow back into the pond so the water in the pipe is at pond level when the power is off.
One more reason to have an aeration system.....
