My house is on 5 acres with the back sloping off to a flat spot at the bottom (probably about 1 acre). I plan to make a field down there. I live in a pretty remote area tho. Not too many neighbors. Lots of tall sagebrush for natural bunkers and such.
I must say, the easiest thing i have found is to use the resources you have. Years ago me and family built a field in the woods; naturally we had to clear small trees which we used to build the bunkers. We would cut them into lengths and pile them strait up on trees. If you need to then use nails or something to keep them up. if i get around to it i will post pics.