I do not think that there is anything you can do really. Nothing you can do in terms of plants or fish.
Check out some type of full chain link style enclosure around the pond. But that would destroy the ambiance of a pond!
Then your target has to be the Raccoons!
This past summer, I was plagued by woodchucks! They finally ate my container grown tomato's. They ate the fruit one night, the whole plant the next.
So this year I hired a Wildlife renewal service. I bought a Hav-a-Heart trap from them. $40 When I caught an animal, they came and relocated it for $80 each. 5 woodchucks, one possum and a squirrel later, I beat back the woodchucks. I ate my tomato's! But I just saw one back in my yard the other day. I assume I will do this dance again next year!? Either that or no tomato's.
Was this cheap? No! But it provided relief. Maybe this is your solution???
Good luck!