honestly get one of these filters
http://www.walmart.com/catalog/product.do?product_id=10291763
and then build your rocks up around it, you can take off the hook that it hangs on the tank from just use the suction cups and the rocks for support and then build up the rocks around it so that it cascades down it gracefully. My buddy had done it in his turtle tank and you can disguise the filter pretty nicely with plants and rocks. Give it a try the filter is only about 20 dollars so what is there to lose? besides 20 dollars which would be cheaper than a pump anyways.