Deter big birds?

A few years ago, I dug us a koi pond. Early this spring, a couple of birds started showing up. At first, we were like "awwww cute birds". But then we quickly realized that they were eating our kois. I've been shuing them away with a stick... imagine a crazy old man waving a stick...Anyway, those birds kept showing up while we're not around and now my koi pond is empty...Those damn birds have even gone as far as catching a hold of my large turtle and try to lift it off. I managed to retrieve the turtle from the neighbor's yard.We're going put in new fish, I guess. Any idea how we can keep those damn birds away? They're huge birds. Here's the culprit.

What if I eat them after I put 60 bullets in them?

Soup...Edit.Good news, guys. I was out earlier today cleaning the pond. I managed to find a single small gold fish, thus proving once and for all the theory of evolution. This gold fish has been hiding in some tunnels I made for the fish. Progenies of this little guy will carry on the hiding gene and will survive the next heron onslaught.Edited by Taz, : No reason given.