we have found that dog rocks works for us. they share a water bowl and we put new dog rocks in every 5 weeks.
the improvment is great. we have no burn marks at all!
however....bianca kicks up clumps of grass every time she wees - so we might not have burn marks, but we have clumps missing all over, and she brings the bits of grass and soil into the house!
ps - i now buy my dog rocks from a guy off e-bay at much less than the pet shops or direct from dog rocks themselves.