Could any one please tell me how do i close an infopath form, so that its not editable for the second time.?

the requirement is :
i have an infopath form used in a workflow. when workflow runs, an infopath task is created in a task list. This infopath form have a submit button, once the submit is clicked the form should be closed and should become non-editable.

I have used the rule: close this form on submit button, but it still allows me to open and edit the form second time. how can i stop it??

any help is highly appreciated!!!