fish pond predators

[Lrptls]

outside we have a small fish pond, we had 6 large gold fish in it and now they are all gone. wev had them about a year, they were fine last summer and they were in a fish tank for the winter. but now things are eating them. i would guess its a few things but the one we witnessed was a duck. we have alot of things around here, different birds that eat fish, raccoons, cats and so on. is there any thing we could put outside to scare them away or is there any thing else we could do? thanks for any help (and i know there just gold fish and we are going to buy more but my grandparents got atached to them)