Time to join a koi club and do some research on koi pond systems. In a koi pond...rock and plants go on the outside....just koi on the inside.
Koi are large riverine carp...not small tropicals. Water gardens are more suited to housing goldfish and gambusi (skeeter fish).
This thread is full of world class koi ponds.
For My Friend Jan T - KoiShack
Few of us can do ponds like these...but they are our inspiration.