Here is a quick solution for you:
on the page or post you want to add a post footer create a new custom field named post_footer
and in the value add the footer content.
then paste this code in your theme’s functions.php file
add_filter('the_content',`my_post_footer`,99);
function my_post_footer($content){
global $post;
$footer = get_post_meta($post->ID,'post_footer',true);
if ($footer){
return $content . $footer;
}
return $content
}
and you are done!
This way you can have different footers on each page/post and none at all if you don’t want it.