That's what I was thinking. Could be as cheap and easy as building a wooden frame with clear or opaque plastic attached to it. Make it into 2 or 3 sections that way it would be easy to take on and off.
With the exception of kois, I'm also not a fan of pond either, but it may work well with clowns. I'm thinking in regards to lighting, that for a clown pond I think it would be better to use those inexpensive submersible LEDs sold all over Ebay rather than overhead lighting.
A cover was my original plan. However I never got the chance due to work etc, we moved into another flat on the ground floor within 4 months so it served its purpose. One day I will build another pond in a more suitable room