[PapaBear]

If you want a Koi pond, leave the rocks on the outside. If you want a watergarden, go ahead and put them in.
Nobody on this board would ever advise putting rocks in a pond because everyone here appreciates the beauty of Koi and the proper care of them. There are a lot of boards (and pond salesmen) who call folks like us Koi Snobs. What we really are is people who enjoy our Koi too much to compromise their living conditions by causing them injury or disease by promoting an improper environment.
Do some searches here on filtration and rock bottom ponds. You will learn a lot from people who have been keeping Koi well for many years.