Bounding width when we give users' TinyMCE or FCKEditor?

I finally got TinyMCE to work beautifully and now am trying to understand how I will bound my users' from not pushing the HTML beyond the borders that I grant them.

For example, if I type;

9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999

It goes off the edge of the <div> space I have defined for this element. Is there a way to still grant them the HTML they produced as a result of using this editor and keep them from going off the edge?

Thanks, David

What I have is something like this in my css:

.post-message {   word-break: break-all; }

That does it for me...