How do you prevent Google Music from importing all .mp3 files on the device? I'd like to have several audiobooks and/or podcasts on my Nexus 7, but every time I put any MP3 files onto the device, even if I make my own folder for it or some such, Google Music detects them and then adds them to its list of files.

This is a problem, because I'd love to be able to use the "Shuffle All" feature, but then it ends up shuffling in chapters from the Audiobook. I don't want it to do that at all.

Any advice?
Well despite the comments about a .nomedia file not working in the newest version, on my fully updated Nexus 7 (as of April 2013) using a .nomedia file prevents the audiobook files from being scanned and listed in Google Music.

Some extremely simplistic testing seems to indicate that a single .nomedia file at the top of a directory tree is enough to prevent all sub-directories from being scanned. In the case I talked about in my question, a .nomedia file within the "audiobooks/" directory would prevent all books from being scanned, even if each book was a collection of .mp3 files within its own directory.