Firstly, does your pond have a filter?
Any pond that is going to have live stock, needs a filter
As for goldfish, yes they will eat plants, they are omnivores after all! I'm not sure which plants they'd be more inclined to eat though.
What do you have in your pond?
The only plant I know of at the moment, is Elodea, which I've seen my goldfish nibble at, but because there's plenty of it, she can't possibly eat it all