Promise Date Set up & madantory Field

Hi

We measure performance on shipment based on promise date, we need to get the promise date field as madantory field, sales user can not book the order if promise date is blank, as on date set up is like that promise date & Schedule ship date is independent to each order

can any one answer how to make promise date madantory ,sales order should not be booked if promise date is not  enetered

Naresh Singhal