I would advise against koi in a soil/clay bottomed bottom for another reason. They are nothing but fancy colored carp and will make your pond a muddy mess in all likelihood. Unless stocked at low numbers and kept that way. Koi often do become bird food, but I wouldn't count on them to manage your pond. Koi tend to evade predators better in bigger ponds as opposed to small plastic formed pond common to backyards.
