[pct-l] Protective tarp under tent

[Mike Yanasak]

I recall a conversation here a while back concerning placing a lightweight
tarp on the ground beneath one's tent and ground cover.  I didn't pay much
attention then, but I recently read a hiking book by Karen Berger in which
she *strongly* recommends doing so while in the desert in order to preempt
having one's air mattress punctured by an evil cactus spine.  I have a
NeoAir mattress, which is made of very thin material and could easily be
attacked and disabled.
Any thoughts?  If so, what might one use?
Amuddler