Want to restrict the Purchase order release at lower level...

Dear Friends,

The Problem i am facing is that the release strategy defined in Purchase order is such that it will be released by four authorities,

& When 4th One, The Highest authority releases the order it should not get unreleased by lower level authorities.I want to configure this.

Partially it is completed, as if Tcode me29n is used for cancel release then it is restricted by Going into

SPRO-MM-Purchasing-Purchase Order-Release Procedure for Purchase Order- Define Release Procedure for Purchase Order

& suggesting it there.into Release Indicator

But still it can get unreleased by Tcode me28.

Kindly Suggest,

Gaurav Chopra