Shallow structure is important. Unless you aerate enough to keep the water autonomous during summer, the bottom layer won't contain enough oxygen to hold fish, so structure placed there might not get used.
Also, you might consider getting some pond plants for YOY fish to hide in.
I believe we're getting some oxygen from the spring that flows into the pond and after this picture was taken we have placed rocks at the inlet and outlet of the piping to help produce more oxygen. Not sure how much oxygen is in the pond or how to test.
