OT: Lockable shelf with wheels

[RGould8 at aol.com]

I'm looking to buy a "librarian cart" type of bookshelf, with wheels on the 
bottom, so that we can roll bookshelves into conference-rooms filled with 
software development books and DVD's.   Does anyone know of a good company that 
makes such a "rolling bookshelve", but with a means of covering the 
shelf-contents under lock and key when not in use?

The closest thing I've found to date are rolling kids shelves, which stand 
about 2-ft hight and fold together (inward like a "V") for security, but that's 
not really tall enough for adults.   It would be nice to have something like 
that, but about 4ft high or so.