megamonster912 on "Ignore post instead of creating slug."

I've been playing around with the post.php file changing slug format for posts with identical titles. But I really want wordpress to refuse the post entry into the DB if the title is already used. Is there a simple way to do this?
I tried the return; instead of suffix but that only resulted in creating a new post using the same slug. If the title is already being used I don't want it in my db again nor do I want a slug added to it.