Large or small? Koi ponds are easy. Google videos on how....but let me warn you, that if you have wildlife around, you are creating a fish buffet. To protect your fish, you either need to have steep sides on your pond (like 2 ft), or you need some protection over the top, like netting, wire mesh, etc. I lost hundreds of dollars invested in koi to sneaky racoons. The chicken wire "protection" made the pond look like a war zone. Not peaceful. I am trying again this year. Pet shops sell feeder fish, (baby koi carp) about 1-3 inches long, and they are CHEAP! I bought 30 1 inch fish, and now I have 30 five inch fish! I just hung a tank filter over the side for now. I turn off the filter at dark, so the night hunters can't smell their way to the pond. To keep the fish happy, the water needs to be circulated , and they need rocky shelves and hidey holes on hot days. I sometimes put the mister over the pond to cool it, and my fish love it! Best luck to you!