We had the same situation happen to our pond several months ago. A raccoon destroyed all of our water lilies when standing on the pots to catch our fish. We have motion sensor lights installed in our yard, and this did nothing to deter the raccoon. We tried netting and it did not work at all.

It was chewed right through and he got all of our medium and large fancy goldfish and koi. Luckily a handful of the smaller and faster fish survived. We never tried a motion sensor sprinkler because we didn't want to deal with the dog getting sprayed or ourselves. But what did work for us was one of those alligator decoys with the glowing eyes.

After putting our pet gator in the pond we haven't had any problems since. It's actually only a fake head of a gator but it looks very convincing especially since it moves around the pond because of the filter. It looks like its actually swimming. Our gator also keeps geese away as well. Anyway I hope this hopes save someone else's fish from being eaten!