Is there a setting to prevent the modification of goals by employees once the manager has submitted?

Hey,
My client and I are looking for a way to prevent employees from changing their goals after the manager has submitted the goal validation document (a perf doc).
Here's the five-step process for validating performance goals:

1. The employee enters his or her goals in the Goals module.
2. The goals are retrieved from the validation document(doc of perf) via the “Update goals” action.
3. The manager and the employee can adjust the goals in the validation document (add, modify, delete).
4. The manager submits the validation document with the finalized goals.
5. The employee signs the document.
   We expected that after step 4, the goals could no longer be modified by the employee. However, we found that, even after the document has been submitted, the employee can still modify his or her goals from the Goals module, and these modifications are automatically reflected in the validation document (perf doc), without the need to use the “Update goals” action.