The best way to incease your O2 levels from a waterfall like you're describing, would be to find a way to take the anoxic water off the bottom of your main pond, then make your 10 X 10 pond full of cattails or some such other macrophyte. This will give you both increased oxygen and trap some of the nutrients. This will also improve your carrying capacity of the .25 acre pond.
Another benefit is that your water will be clearer with this type of filter. I am using one right now to keep 100 fish in 2 X 100 gallon stock tanks. The difference in water quality before and after the filter was amazing.
