This falls under the catagory of "Not my strongest suit", so don't take my word for it., but the only thing that comes to mind is Explosives.................Man, can I come over to your house to play??!!?..........
I would have to assume that the Jack-hammer you used was one of those rental ones that run on electicity. Those don't hold a candle compared to air-driven hammers, like you see contruction crews using on highways. They also cost an arm and a leg to rent. Might you consider doing some creative landscaping around the piece of rock?