In1978 the copyright laws were changed. So, your work is protected by simply printing "C" with a circle around it and the year date. Example C 2007. Defending the copyright if there is an infringement may be a different question since it is generally expensive to defend your work. However, if your work is stolen, it is very easy to defend IF you have also "Registered" your work for a fee with the Copyright Office. That is also an expense you must consider. Generally for articles or newsletter content, it wouldn't be worth it. On the other hand, the name of your newsletter or magazine that you own may be worth it.
Personally, I have never bothered "registering" any of the articles for magazines I have written although I always include the "C" with year with everything I have submitted. The magazines I have written for have seemed to protect my work. The books I have written have also included the "C" with year. Only once have I had to write a letter to somebody telling them they have STOLEN my work. That person wrote me back and told me they would correct their error and give my work credit. My work is now an obscure reference in somebody’s list of references.
Good luck with your work.