How to restrict "posting date" If They use previous date

How to restrict “posting date” If They use previous date

1.Document No is— PO/11/00079, posting Date–03/14/11,(this is my posted document “purchase order”)

2.Document No is— PO/11/00080, posting Date–03/12/11,(this is my Current “purchase order”)

it has to check Posted “PO” and i want to block if they use previous posting date -----

It depends on what documents you want to block. In any case, select the No. Series of the document you want to block and place a check mark on Date Order flag.