I'll second on the bog filter!
I'll be doing a bog filter on a relatively large backyard scale pond (~3000 gal). The bog will hold roughly 10% of the overall volume (roughly sized 6x6x2). Whats better is that it will be doubling as the upper basin for my waterfall/stream back down to the pond. I'll be using a 5200gph magnetic submersible pump, fitted with an easy to clean DIY pre-filter, to pump the water up to the bog (10 vertical feet, thus why I'm using a 5200gph pump... it has about 3000gph @ 10' head). Haven't entirely decided on the plants I want to use, but I still have a touch of time left to do that. I'll explain the basic details of how I will be creating the filter. You should be able to scale it down and do the same.
Water is pumped in to the filter from the side, about 6" up from the bottom. This bottom 6 inches will allow for sludge to settle. I will have a bottom drain that I can open to wash this sludge away. Egg crate or similar will be used to create this 6" open water area. On top of the egg crate will be varying layers of gravel or lava rock (I personally haven't decided). I will top it off with some fine gravel, coming right up to the top of the water level. Plants will be planted directly into the gravel. No soil needed. Finally, I will have the bog excavated so that the water will flow up and over the waterfall (i.e. the waterfall will be a low point).
I hope that explained it enough. I should note that this isn't exactly how I will have mine. I am partitioning off a small area so that I have enough water available for the falls. I will also have a valve that will allow me to send the water from the filter to the pond directly and bypass the waterfall, but that doesn't have any bearing on the bog filter directly.