Are you talking about the GET variable id?
You want to pass variables via GET, but hide them from a user?
The very nature of passing variables via GET requires them to be visible in the URL.
Just find another way to pass your variables.
The only possible way to pass a variable without the user having access to it is using $_SESSION variables, or maybe POSTing variables using fsockopen.
Just create a session, and pass the SID if you don't want to rely on cookies.