I'm with pondlady on this. As I said before, get a bigger pond.
I know you said space and cost. Your labor costs you nothing and an EPDM liner for a 700 to 1000 gallon pond is about $200.00.
If you can't go down or wider, then how about up?
I have friends with small ponds and tanks that have Koi. I do free exchanges with them when the fish outgrows the space. I give them choice of my baby Koi in exchange for their larger one. It is a win-win situation.
Maybe you can find someone near you to do this with.:7_5_1311: