I have 4 cedars (6 - 8') in my .7 acre pond. I drug them out until they were submerged and that is where they lay now. They sure do attract the BG, which sure does attract the bass, especially when I am feeding. I don't KNOW that I did it right but believe that any tree put in the water will last longer if it is completely submerged so mine are about 18-24 inches underwater with 1 cinder block attached. One of the experts will surely give you a better answer but I seem to remember reading here that 15 or 20 percent of your pond should be cover.

PETA, People Eating Tasty Animals