A koi pond is usually constructed about six inches above ground, and four inches deep. The pond should be built where there is no direct sunlight all day. Use brick or stone to construct the wall and use a quick drying cement to hold these bricks together. Smooth-en the pond and use a bird net over the pond to keep away birds that hunt the Koi. Install a properly sized water pump, filtration system, and an ultraviolet sterilizer, and then add a protein skimmer to reduce the organics causing foam. Never put chlorinated water on the pond as this will kill the Koi.