I have some rental property that I am tired of spraying roundup on and it only lasting 3 weeks or so. What is a good product that will kill everything and last for awhile. I had a gallon jug few years back that a client gave to me, don't remember what it was called but it was purple. Where I sprayed it burned it off for over a year. You could not even get bahai to grow back in that spot! Pesticides and herbidices are not my expertise since I will not spray it for any clients until I get certified.