Preventing Double Submission of Form

Preventing a user from submitting a form twice and creating multiple entries server side, is a common problem online. I didn't see feature for Gravity Forms to prevent this. So I've tried to figure out a way to use Hooks and Filters to accomplish this. I've read some posts on this, but can't figure out what to do. Nothing seems to work. Anyone have any ideas?

My two ideas for code now are as follows (why don't these work - nothing happens when I submit the form):
IDEA1 (Javascript)

function pre_submission_double($form){
?>

<script type="text/javascript"><!--
function doSubmit() {
    document.gform_1.gform_submit_button_1.disabled = 'disabled';
    document.gform_1.gform_submit_button_1.value = 'Processing. This may take several minutes...';
}
//-->
</script>

<?php
}
add_action("gform_pre_submission_1", "pre_submission_double");

IDEA2 - just change name and maybe add CSS
-----------------------------------------------------------

/* Try to Prevent Double Submission by changing name of buttton*/
function pre_submission_double($form){
    //rename button after submission
    $form["button"]["text"] = 'Processing';
    //returning modified form object
    return $form;
}
add_filter("gform_pre_submission_filter_1", "pre_submission_double");

Thanks, I was not aware of the No duplicates feature, but this does not really help us, because our users upload files to the site and if they submit the form twice the same files get uploaded. I have read elsewhere that you can add custom javascript to the submit button, something like "onSubmit" - but I cannot figure out how to use "gform_submit_button" filter. The documentation is very sparce. All I want to do is add an onsubmit function to the submit button. Would I just copy my submit button exactly as it is and just add the onsubmit to the string?