We have not had any pvc damage from gophers, or anything else. And we DO have gophers... right now, they are tearing up what is left (after not much water the past several months) of our back lawn.
The drip and the netafim are problems, though. And the chewing damage is undoubtedly from rats. Our city (which prides itself on the number of trees, to the point that I think of City Hall as "Tree Nazis") is Rat Haven - at least in the areas with larger properties, and thus more and larger trees. In our neighborhood (1/2, 1, and > 1 acre properties), probably half the large oaks have rat nests in them. Our arborist takes down as many as he can find (including on the neighbors' property) every time he comes. (And it's not just the trees... we have found rats nesting in hedges, in our in-ground water valve boxes, and most recently, in our bbq!
)
I haven't been up to Lake Tahoe in years, but I go up to Yosemite and the East Sierra early most autumns. It was looking pretty dry up there last year. Last fall, when I was taking a break at one of the Mammoth Lakes (I had hiked there), I overheard one couple telling another couple that they had met some hunters earlier on their trip. These hunters apparently hunted the same area(s) every year (fall), and depended on certain creeks to supply their water. That fall they had started off on their hunting trip, but when they discovered that the creeks that they depended on for water every year were dry, they had to turn around and go home.