Need required fields in New Post page!

Multiple authors on same sight…

Admin needs assurance that authors are filling out Excerpt fields, as well as other items (Category, Content, etc…) before they publish new posts.

I have tried various methods of WP_error without success, I just cant seem to hook onto publish_post based on the entry or lack of entry in these fields and stop the post from being published. I just want an error message to display similar to form validation.

Any ideas?