The pit does not have any magical properties. What turns the guac brown is the air. If you can keep air from touching the guac then it will stay green. The pit will keep a portion away from the air, but what is more affective is to put plastic wrap over it and push it right down onto the surface.
In my experience, denuded skin is when the top layer is off, sore is very superficial and usual caused from a shearing force. As above, there are many taypes of foam backed dressings used in teh VA, depending on which VA you are at. I am familiar Allevyn but here is a site where you can compare.
What is the matter of air leakage during cupping? Ans: The causes of leakage of air or not sucking on during cupping are mainly; the time of use is too long, the aging of rubber stopper or dirty substances absorbed on the rubber stopper; dryness of skin; hairs too much or too long; incorrect use of vacuum gum; insufficient air exhaust in vacuum gun, and others.