Stopping people from moving on

I assume you mean that you don't want people skipping to page if they know the url thus bypassing the earlier stuff.....I would need to think about this a bit, but on the face of it I would create a variable and update it as the user progresses from page to page. I would only allow them to advance to the page if the variable had the value assigned by the previous page. That would require a conditional action, but should work.