Ok, I'm fed up with the "over the counter" weed control. I NEED HELP!!!!!! I put in a brick patio and USUALLY I pull the weeds as they come up. But I have two little kids and I'm running out of time for weeding the patio. So I bought some concentrated Round Up and sprayed it twice and SOME of the weeds died, but not all. I even doubled up the mixture. Anyways, I need a good solution for killing these weeds without coloring or staining the bricks. ANY ideas?