Apparently the privacy fence has been covered on both sides for about 16 years now without excessive degradation. I couldn’t remember when it was installed, but in the list of Related Discussions at the bottom of this page was a thread I started in 2009 talking about that very thing.
And it seems the neighbors’ fence was originally installed to contain their pit bulls, rather than screen off their hot tub (they added some tall plantings when the hot tub went in). Nowadays there’s less discussion of pit bulls on SDMB, but as it turned out the male pit was a dangerous bastard, and the female (Tillie) was sweet as spring flowers.
Finally, alto the double-sided fence is weathering fine, the 3.5” space between the sides is a convenient highway for squirrel traffic. Which is no big deal.