So I'm making an ~200ft long zip line with the top being anchored to a tall tree in my backyard. My problem is I need an anchor for the bottom. Can I use a 6"x6"x12' plywood buried 4 feet in the ground with a guy wire anchored to a 4"x4"x4' 2.5 feet into the ground? What would you say I should use to anchor th zip line about 4-7 feet off of the ground? Note: I can't find any used telephone poles near me so you have to come up with something else besides a telephone poll.