1. If you live in an area with winter snow and ice, the pond has to be deep enough for the fish to survive below the ice. Most say that the pond should be 24" deep or more.
2. Most ponds attract wildlife such as raccoons. Raccoons enjoy fishing, like many humans, One spring we put in 20 small goldfish and by autumn there were only 4 left. Thus we have stopped feeding the raccoons and no longer put in fish.
3. If you have fish, the bottom of the pond may have to be cleaned out to remove their droppings.
4. Raccoons also enjoy plants and other floating things in the pond that they can reach. We have yet to have a bloom on a water lily after 10 years as the plants are destroyed before any bloom. We then stopped putting in plants and instead put in small floating glass balls and other small ornaments. One day a plastic frog that was floating on the pond was found a week later on our roof. One year we put in 20 small floating glass balls (1" diameter) and by autumn only 1 was left that was not broken or gone missing.
5. We now have no fish, no plants and no small floating objects in the pond. We still have a small pond but only put in larger floating glass, similar to Dale Chihuly glass balls, and this seems to work (although we do find raccoon paw prints on the glass balls).