[Zope] Cookies for banishing users

[Chetan Kumar]

Hi all
The situation
1. The user logs in and the cookie is set.
2. The user requests a page with a form and submit
    button
3. The page contains a request to a python script
4. The python script adds data to a SQL table
5. User is redirected to a "thanks" page. The address
    bar refers to the script (not the "thanks" page)
6. The user logs out (The cookie should expire here)
7. The user clicks on "back" button to come back to
    "thanks" page.
8. The user reloads.
At this stage another entry is made in the SQL table.
I want to put an end to this behaviour of the site.
The user should not be able to insert data by just
reload.
My question is: Can cookies be of any use here.
The problem is that unless the user closes the
browser this is not unset. The user is not able to
see other pages but can activate the script !!
TIA
Chetan