after logout user can not back browser button

hello all,
My problem is after logout user can't back the browser button ,
I want use this code but not properly .
code here....
<script type="text/javascript">
function noBack() {
window.history.forward()
}
noBack();
window.onload = noBack;
window.onpageshow = function (evt) { if (evt.persisted) noBack() }
window.onunload = function () { void (0) }
</script>



plz help me.......
thankx
...