David makes some great points. I'll share my strategy. It might be different than others, or maybe not. With auditions and demos, you will often get the whole script. particularly if it's for a 30 or 60 sec ad. What do you do to watermark your intellectual property without making it unpalatable?
For those unfamiliar with the term, watermarking is a term from digital photography, in which the creator has some type of logo inserted into the image so the client or viewer is aware the image belongs to someone. You can them contact the creator who will have the clean version. With VO, you can watermark your reads a number of ways. One would be to change the wording so that the client gets the jist of it, but you will obviously have to record it again.
You can record only a portion of the script. The is fine for longer demos, but for shorter ones, it is hard to justify.
Adding a sound effect like a metronome or some people even add their own voice quietly whispering this is a demo, which will make the demo unusable but sometimes unpalatable.
A further option, and the one I tend to use, is to grab some royalty free music from the internet. (Google, young grasshopper, Google will find it). You have to make sure it's royalty free or you could get in trouble for copyright. I will then lay the track underneath. Again though, this has pluses and minuses. You need to be certain the music matches the feel the client wants. You have to make sure the music doesn't obscure your voice. The other issue that might arise that you aren't aware of is occasionally the client already has music picked out, and often just plops your voice demo over top to see how it sounds. Tough to do if you already have music.
But if I have time and I like the demo, I'll do a little extra. It's fun for me and I keep saying, if I'm not having fun, why am I doing this? If I'm not enjoying it, why am I doing this? So make sure you enjoy everything, especially the demos. Get creative. think outside the mic...er box...
on a side note, a great use for music is to help you do a better read. Or a different read. You'll need close backed headphones with the sound not too loud that it bleeds into the mic. Got a dramatic read? Throw on Carmina Burana and go to town. Or some sad banjo, or happy banjo, whatever will get you in the right space to do an awesome read. It can also help with the tempo of your read.
hope someone finds a useful nugget.
Cow Bella