we have at least a dozen arborvitae along a chain link fence which borders our yard. Over the last couple years they have incresingly been losing a lot of their foliage, to the point where some may be dying. The neighbor has water issues which he has never really addressed, (his property runs higher than ours since we live on a hilly street), and we get water run off from his yard. Another problem may be from willow type trees right next to his house (there were 3, one remains) which may give cause to root problems we can't see. Any suggestions?

If they have been doing well up until a couple of years ago and if external factors have not changed, plants could be failing due to old age, lack of vigor, environmental stresses from doughty summers or extremes in temperatures. Plants can fail over a few seasons after a hard winter or severe drought for example, so it is harder to make a direct cause and effect diagnoses. you might also contact your local extension office for a more local and focused reply.