Make absolutely sure there is a link somewhere on every page that returns visitors to the home page AND draws the entire frame:

<a href="index.htm" TARGET="_top">Home</a>

You can also handle out of context pages by adding some simple JavaScript code to all your framed pages:

<script language="javascript" type="text/javascript">
<!-- Hide script from older browsers
if(top==self)
{self.location.href = "index.htm";}
//-->
</script>

This checks to see if the individual page has been loaded outside the frameset. If so, the script directs the browser to load the top-level frameset instead. This particular script always delivers visitors to the same frameset, no matter which page they were trying to view.