Purchase - control Documents

 Dear All,

we have created Purchase Order of qty 10 , against receipt & delivered of 5 qty

now the user cancels the PO , system allows to do it

we need to stop / deactivate the funcitionality of CANCEL PO ,

cancel button can be done by Form Personalization

but system allows to cancel from "Control Documents" ------> how should we control this

or is there any system setup / profile option that if full/part receipt is done  against PO , system should not allow to cancel the PO

Regards

Manish Shheth