the late Tony Treadwell used cooper sulfate (root killer in a rural hardware/farm supply)and got great results

http://www.lulu.com/gb/en/shop/tony-trea...t-20115603.html

the only warning - at least the early versions of the book had a mistake- and said two cups (actually said mugs) of it - his website said three tablespoons- the heavier concentration will over etch