Sessions in ASP.NET For Login.aspx Forms

1.If the login info is correct then it will redirect to dns.aspx.
2.In dns.aspx in Page_Load i check the condition like...
if(Session["user"]=="Yes")
{
//do something
}
else
{
Response.Redirect("/dns/Login.aspx");
}
3.Now if i click the logout button i redirect to the user to login page and set the session variable to null like...

Session["user"]=="";
Response.Redirect("/dns/Login.aspx");

But the problem is that if i click the logout button and if in browser if i click the back button i am able to see the last page i visited without loging in. So how to fix the problem.

Thanks,
Swami

You can use the following, to disbale the browser caching in your ASP.NET pages:

Response.Cache.SetCacheability(HttpCacheability.No Cache)