This is our 12th year we,(my hunting partner) have been doing this.What we have found is to keep the box height at 6 to 9 feet high over the water.We make our boxes 8" deep,11" high,10" wide. Use an oval shaped entrance hole of 3"x4". Make sure to put some drain holes in the bottom,we make 4.
Use metal around a wooden pole at the top,or just use a metal pole. We put these up on my partners property,which is agricultural and marsh land. Remember to have an access door for cleaning later in the box.
As far as the "Hills" go,there just mounds we make about 2 feet out of the water,about a 3 ft diameter.We use rocks and wood to build up,then cover with dirt. Lots of different birds use these for nesting.
gooser