Ouch! It's sad and interesting how many of these events are not actually caused by maliciousness, but by ignorance.

We're concerned that a drainage ditch would be a massive undertaking because of the general runoff pattern from the entire hillside. We've already seen how the foundation of a house built 200 yards uphill from us has slightly changed the groundwater flow to where we now have a "swampy patch" at the bottom of the back yard... which I will have French drain to keep from becoming perpetually standing water during the wet season.

We've now hung prayer flags on the fenceline, and added actually "Please do not spray chemicals! Food garden below!" signs in a couple of places.