The amount of sun is very important. If that is a deep shade area it requires a whole different set of plants. What is on the other side of the fence? How much room do you have between the fence and pond rocks?
I can envision some evening primrose or forget-me-nots in hypertuffa pots or troughs on the rocks or among the rocks around the pond. Can you post a picture looking at the other corner?
You have a lovely set-up. I would add some water lilies of some type, because I love water lilies.