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.
Due to the action of plate tectonics, compression, stress and shearing forces over long periods of time, rocks can be essentially warped and deformed, causing them to be compacted into a smaller volume of space.