If you're interested, I just launched a service which helps with this exact problem (watermarking of music), It's called TrackTrack.it. It works with a number of file formats (wav,mp3,mp4, ogg, flac, aif) but, full disclosure, there is a conversion process.
Anyway, if you send your song to 30 different people, they'll each get a uniquely watermarked
copy, which is inaudible, so if it ever shows up on a file sharing site you'll know exactly whose copy leaked.
We do a ton of other things, too. You can send songs from your iPhone, track to see if a person listens to a song, send streaming only links, see where (on a map) they listened to the song, etc etc. And it's SUPER easy.
I hope this doesn't seem too spammy, but I'm a musician, originally, and I got sick of all the leaks in the industry and thought that it'd be nice to fix it!
You get 30 sends for free, check it out I think you might like it. TrackTrack.it - File Sending for Music Professionals