I have decided to make my own filter for my pond. I will be using a large Rubbermaid stock tank to allow for a lot of media. My idea is to have a 2 inch inlet on the side near top and have the water trickle through a plastic plate with dozens of holes. This will allow for good coverage. After trickling through pads running from coarse to fine yet another plate with holes to allow for water to trickle over media be it bio balls, lava rock etc. My original plan was to have the water return to pond via 2 2 inch outlets located at the lower half of the tank. I have a couple of questions: 1. I see many home made and commercial designs of this type of filter where the water inlet and return are both near the top. Doesn't this negate the idea of a wet/dry since the media will be continually flooded and therefore have less oxygen for bacterial growth? Or has it been found that keeping the bio media wet does not result in decreased efficiency. In my aquariums I always used wet/dry so am thinking the same applies to a pond. On the other hand I have seen immaculate aquariums which utilize a canister filter. 2. Secondly, I am strongly considering a small waterfall to allow for oxygenation and relaxing sounds. Originally I was going to simply place filter by edge of pond, hide behind bushes and have water return directly to pond. If I build a waterfall and have the outlets near the bottom I may have an issue as far as how to hide a 100 gallon stock tank at the top of the falls. If I were to have the returns near the top i could bury the majority of the tank and problem solved. My only concern is the possible decrease in efficiency if the media remains wet , which it would if the returns are near top. Am I over thinking this? In the end will submerged media be a problem? 3. lastly, in my area the earth is all sand. I am concerned about how to build the falls. If I had a clay mix no problem. With all sand how will it hold up over time? I understand the concept of sculpting a pile of sand to the desired contours and laying liner followed by rock but will it collapse over time? If i have only sand to work with should i construct some sort of a retaining wall with cinder block? If so it will be quite a job trying to hide the cinder block behind stone and flat rock.