Web Forms :: Browser's Back Button And Cache?

Not sure if i'm posting in the right forum, if not, please move it...i have the following issue... I want to "disable" browser's back button. Seems it's not possible, but using cache.setcacheability and timing it, kinda disables the option of navigating back. I need this because in some pages of my webpage, i keep values in a Session variable so when a page loads, i need to check that variable, and, if navigating back, cant do that. I also "set cache to false" because if someone closes session, and i allow cache, someone else could handtype a url in that same pc and see the page without login (though if he/she tries to navigate through it will be kicked out because when loading a new page, i'll know that he/she is not logged) but i dont want to allow even that,

that's why cache is disabled. The problem is that loading over and over again my masterpage (header, footer, menu and stuff) is going to slow down the webpage, because every time there's a request, the page has to be sent again completely. So, is there something like a "mix" mode where i can allow cache just for a few things? If not, what's the best practice to achieve both things i'm trying: speed and security?