I am so sorry about your 9 koi.

Maybe next time you can add more large koi, at least 30 centimeters.

Do you have a place for your Koi to hide in the pond? Try creating a cave for them using a couple cement blocks topped with a piece of flagstone or a milk crate turned on it's side. You should also check out the Contech Scarecrow. It is a motion sensor device and it does a great job at keeping many types of predators from eating your fish.

i had a great blue herrion raiding my pond. (i hope that sob choked) untill i put up fishing line on stakes, crisscrossing my pond in an irregular fashion. high, low, across, around. use line that's as clear as possible, but strong. it's not pretty, but it works.