Monitor the water level of your pond, as hard frosts can cause defects in the liner and in concrete structures. If the water level drops considerably, then it may have developed a leak. Be sure to keep it topped up until repairs can be carried out in the spring.
Rake out fallen leaves or shake off those that have gathered on protective netting.
If you have koi carp or gold fish, use pond heaters, air pumps or place floats on the surface of the water to keep it from freezing over as this can be fatal for fish. To make a hole in frozen ponds, hold a saucepan of hot water on the surface until melted through. Do not crack the ice, as this is harmful to fish.
Unless there is a build up of rotting waste, wildlife ponds (with few or no fish) do not usually need to have a hole made in the ice as there will be sufficient oxygen produced from algae and other plants below the surface for pondlife to survive. Where safe to do so, brush the snow off the ice to allow light to reach the pond.