Restricting the change or display authorisation of quotation

Hi,

Once the pricing is done at quotation level. It is sent for review to head of department. He will add some profit margin by adding another header surcharge on it. Once the quotation is saved by the department head, no one else can change or display that quotation with the help of restricting the authorization.

How can I restrict the even the original creator of the quotation (Estimator) as well as others from seeing the quotation. Because once the profit margin is added by department head, they want to keep it secret. Is there any user exit for it?

Regards

Suman