Hi Mark,
Your concerns are very much true and unfortunately there is no absolute solution for this issue.However, the following might help you face and handle the issue:
1. Use Google authorship.
This will help the search engines recognize the correct or the rightful owner of the content. Here you go for more:
http://www.google.com/insidesearch/features/authorship/index.html
2. Have the copyright notices published along with the content. Give clear syndication guidelines like, an attribution in the form of a link pointing to your webpage (that the content resides on) if someone wants to publish on their website.
3. You can always file DMCA complaints right from the Google webmaster tools account.
4. You can use Google Alerts to watch out for any of your content being stolen and published elsewhere.
Here you go for more in this regard:
http://blog.kissmetrics.com/find-remove-stolen-content/
Hope the above help.
Best,
Devanur Rafi.