I try not to use voice-overs at all. I allow visitors to stream and download full length, low quality versions of my music to enjoy. After all, I specialize in creating moody instrumental music - not moody vocal music.
Unfortunately, there are many people out there who do not honor the basic copyright laws and willingly take others' works and promote them as their own. Copyright infringement is very common and there really is no protection other than submitting works to the government for an oficial copyright.
I know that some people will claim that music is copyright protected as soon as it is created. That may be so, but my research has shown that without an official copyright registration, it's hard to prove your ownership in court. The 'poor man's copyright' is a crafty idea, but it doesn't hold up in court.
I create original music daily and I want to share my music with the world. It may sound crazy, but I am willing to give music away in order to be heard. Of course, I want to make money from what I create - that's why I'm in business. But first, my music must be heard - not my voice.
I feel that there's no need for me to protect something that people won't listen to and pass along around the world. If visitors think my music is any good, then I encourage them to download and stream all they want - and come back and get more! If they like it enough, they can always come back and purchase the high quality (CD quality) version. The music consumers should get what they want and they should be able to try before they buy.
Besides, if someone wants to steal my music and claim it as their own, my copyright registrations will back me up in court. If they get rich, I'll get rich too!