Browser Cache and PHP Namespace

Greetings, I had some problems with broser caching behaviors and php name space collision. I do lot of googling and try to figure what happened and I failed to figure. So I need help, Here Details 1-) Browser Cache Beahviors You know the back button problem. I search the net and found some header modifications to fix this problems. Like this ini_set('session.cache_limiter', 'private'); And this will lead the some caching issues. Time to time browser may forgot or misbehave with javascripts. Is there any suggestion for this. When visitor hit back button and previous page has retun data from post variables. 1-) Re posting without any message 2-) No content cache 2-) The another problem was developing aproach. Currently I'm working on large CMS thingy. My project be able to include php files anytime anywhere and unlimited amount. So time to time variable names will collide and it was so hard to detect. Is there any suggestion to avoid these kind of collisions. Thanks Sancar