If the fish hibernate in the pond, you can prevent complete freeze-over by leaving pond filters running or fountain and filter pumps, respectively, this will help keep part of the surface free from ice. Do not break the ice under any circumstances!
Water movement keeps part of the pond ice-free. Only turn off filters and water falls/fountains if the weather turns exceptionally cold.
It has been shown that ponds where the surface freezes over come to no harm and can be beneficial. The fish will be hibernating in the bottom of the pond and less active.
Feeding your fish should be stopped by now as the temperatures are dipping.
Even if they come to the surface on fine sunny days refrain from feeding as the fish will be using there fat reserves and will be unable to digest any food that they will eat. This then rots in their stomachs, the gases build up and the fish looks very fat and round, this will kill the fish.