How to Stop Purchase Orders being Deleted

I have recently taken on administration of a Sage 300 system.

We have had an Audit issue where individual purchase orders have been deleted. This causes a problem for audit.

What security settings do I need to stop a user deleting a purchase order and its lines, bearing in mind that they will still need to be able to raise headers and lines for new orders.

Once a header has been created - even if it has no lines, I need to be able to stop the header being deleted.

Does this have anything to do with Clearing History?

Thanks

Andy