If I was doing it, I'd get a pointed concrete chisel at Lowe's like the $13.98 Irwin 3/4" pointed concrete chisel and beat on it with a 2-lb mason's hand hammer, repeatedly, which should break up the top area of that gray granite boulder enough so what's left is below the ground level. ...... have fun.
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... down and out, liv'n that Walmart side of the lake!
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