Another thing you should consider before digging is ( if you're considering having fish/plants) how deep you are going to make your pond. If you want to keep big fat koi in yours like I do
then you probably will want to keep them in the pond year long, throughout the winter and all.
I live in northern Ontario and the temperatures get very cold here in the winter. I made my pond 7-8 feet deep so that it only freezes about 3 feet down, and the fish can live underneath the ice. I keep a little heater in there to keep a hole in the ice so harmful gases can escape and don't kill my fish. I also keep the filter falls running all winter for aeration. If you make it deep enough you can also sink your plants to the bottom for the winter. In the spring bring them back up to your shelves and they start growing leaves fast!! This way you don't have to worry about bringing anyone inside for the winter and your fish will grow much bigger !
you do not have to worry about feeding the fish over the winter as their metabolisms slow down so much there's no need.
I've done this for two winters now and it's the easiest, most maintenance free way.