Editing Complex Pages in Visual Mode

Question

This might be a stupid question, and maybe I've missed some best practices thing, but I've been having this problem with clients using sites on WordPress. Let's say we have a fairly complex page that requires some good amount of HTML code inside the page itself. We put it up and it looks great. Now, month later client wants to edit couple words there, goes in and edits them in Visual Mode, and of course all markup that we did is now screwed up, so stuff is all over the place.

What are the approaches we can use to handle cases like that?