It's not possible.
Even if you do manage to find a way to protect the CD (e.g., by including intentional errors and then using an application to check for those errors before playing the content -- this was tried beyond the point of exhaustion in the 1980s with floppy diskettes on the Commodore 64 for the purposes of copy protection, and every one of those methods was defeated in a variety of ways), people can just fire up a free/open-source application called Audacity ( http://www.audacity.sourceforge.net/ ) to record whatever music is coming from their speakers.
Notice that Apple's iTunes will play a portion of the songs in their store, but then you have to pay the dollar (less a penny) to get a copy of your own. Apple has taken steps to make sure that music stays on the buyer's computer, but there are a variety of tools to get around even this. Although Apple's efforts appear to have been quite extensive, people still find ways to get around their copy protection.
So, you may wish to include a portion of your songs as a sample, but don't be surprised if your music winds up on some torrents or BeeMP3.com, Baidu.Com's MP3 search, etc. (at the very least it could be a confirmation that your music is good if people actually want to share it).