Protein skimmers.. Depends how involved you want to get.. SOme run off of airstones and some are venturi or downdraft venturis. Here is a link to a simple one and some that can get more involved.. All parts can be pretty much be acquired at a hardward store.. I never made one for a pond but I had some DIY ones for my 200G reef tank.
The cheapest is the airstone model. The more involved is downdraft venturis but from my reef days those worked best.
The Info above has only to do with my salt water experience and not for Pond Protein skimmers.
http://www.reefkeeping.com/issues/20...ture/index.php
Joe