My neighbor, who use to work for a road construction company, has offered me a bunch of road pillars. These are the pillars that they use on guard rails/highway barriers. Each are about 4-5ft tall and probably 8 inches in diameter. I am thinking about taking some of these and creating and artifical stump patch etc... How many would I need to bury to be effective? What pattern, ie row, offset, star pattern, etc..? If I buried them 12-18 inches that would leave 3-3.5 feet sticking out of the ground. These things are heavy and treated so they should last a long time.