[plt-scheme] metaphors for local

I'm enjoying these metaphors for closures. But while we are at it, the 
instructors for the HtDP-based course I designed but am not teaching 
this term are wondering about metaphors for local. They want something 
akin to the stack of books on one's desk, or the cache of library books 
on one's shelf. One of them suggested a fresh piece of paper for local 
definitions which gets ripped up (recycled?) after the body is 
evaluated, but I said, hmmm, you have to be careful or you get dynamic 
scope, not lexical scope. So, does anyone have any ideas? --PR