How can an admin create a repository to share rubrics across a department? I want to lock rubrics so they cannot be edited.
You can access the Rubrics tool under the Admin cog. From there, you can create the rubric and make it available to the appropriate department and all the course offerings under it. This shared rubric will not be able to be edited at the course offering level.
You may try to create the rubrics in the Org level and share them with all descendents. With this, the instructor will see the shared rubrics and use them in their courses, but not edit them. And, they´ could create a copy of the shared rubric and save it into their own course.