Pond filter

[Desastre]

So now that I have figured out what type maybe you can help me with some other questions. My friend has had this turtle in his pond for almost two years now. He wants to be able to keep the water a bit cleaner in between water changes. Right now he only has the water pump that runs to the overhead fountain but he wants to add in a filter or make one himself. The pond is 40" length and about 15" height. So I tried to google it and it has crossed my mind that a fx5 canister filter might do but not sure with just foam/polyfil media. So basically
1. What kind of filter system can he use or make. He is a architect so he is a very hands on DIY kind of person.
2. Is it ok to place the canister so far above the waterline im no canister expert as I use hob for my freshwater tanks.

Added some pics to get an idea of it's surroundings. Any information will help as I really want to help him with his filtration issues.

 

[chagoi]

If you want a canister Nu Clear would work. It goes after your pump.

 

[Desastre]

I'n the end he decided to go with this design: http://www.skippysstuff.com/biofiltr.htm I thought it was pretty good for a DIY kind of person.