div wrapper for css

Is there anyway to set the "id" of the inner text area of the html editor so that a stylesheet's rules will apply to it? At the moment I am putting a div tag before and after the content, and then removing it when the use posts eg

<div id="article">
<h2>This is an article</h2>
</div>

and upon posting I insert into the database

<h2>This is an article</h2>

The problem is that the user can remove the div tags and cause my scripts to fail, or write content outside of those tags. Is there anyway to "lock" those tags or hide them from the user somehow?