I don't think you should put the fish in the pond. Try calling a nearby aquarium or pet store; they might accept the fish. The goldfish can affect the ecosystem of the pond.
I have had a goldfish living in a aquarium for several years now and he is getting a little to big for it (the fish is about 12 inches long), and i was wondering if i can put him in my fish pond? If i can how should i introduce him to the new environment? I also have koi in my pond.