I can feel your pain. We had a similar problem here. We are halfway up a hill and as everyone knows water (and other undesirable stuff) flows downhill. This is a third world country where developed countries like to dispose of their mistakes (remember thalidomide?). Most countries have banned the use of 24D, Mecca crop, and Roundup. Here it is being sold in the local farmers market and by street vendors. In 2009 a neighbor decided he didn't like the grass/weeds growing along the side of the road so he liberally sprayed both sides. Needless to say I was not pleased since it leeched onto our property and did a lot of damage. To solve the problem we built a concrete ditch on ourside to drain rain water and redirect elsewhere. Then we built 30-foot walls. It has taken all these years to mitagate the damage done to the land down by the road.