Lets face it: We care enough to bring home a bit of nature, a pond, an aquarium, even making a habitat in the garden for toads and feeding the song birds and humming birds, minimizing sprays to conserve insect populations and using integrated pest management.
This is an open invitation to the rest of nature that we might prefer to keep outside the fence. Raccoons, herons, bears, opossums, skunks and many other less desirable critters are going to try to move in.
A sturdy screen around and over the pond may not look great, but it will protect the fish and plants from these invaders. You can always take it off when you are having a party (unless it becomes a trellis for a vine).
A good dog can help, but mine sleep inside. They will bark if a skunk comes looking for cat food, but the skunk has figured out that there is no cat food after dark. The empty bowls just smell like cat food.
Actually, one of my dogs is quite happy to splash around in the pond, and can do as much damage to the plants as a raccoon. I better keep the wire mesh up.
How about wild turkeys? So far they have not done damage to the pond, just scratched around like giant chickens, and disturbed the mulch. (Careful where you walk!)