Disable user ability to directly make changes to published posts

I am using User Role Editor plugin to set limitations what my users can do in my web.

I have a user role Agent which is able to write a post and save it as a drat but not publish. The problem is that after his post is approved by editor, he (Agent) then can make changes (in that post) and publish them. I want to limit this privilege to user role Agent – so whenever he makes changes to published posts by him, an editor must approve them before published.

Thanks in advance.