I've been spraying with Round Up Pro Dry with great effectiveness, but way too often!!! 2-3 times a month is not enough!! I've got somw Ortho Triox that I tried last year w/ NO success! (Could it be my fault?) I want something that will keep the weeds down for a while, a long while preferably. Soil sterilants sound harsh, but... Any comments / suggestions? PLEASE HELP! I'm loosing time and $ on this repeated spraying!