I was thinking of making one too. I see a lot of people point to this one article, that seems to be a pretty popular one. Looks like an oldy, but that doesn't mean its not a goody. I think this is what you are looking for, I call it a pond box, check it out. Here it is, let me know if you find any others.
http://www.njwa.org/Old/gunningboxplans.htm