Restricted WBS during PO Creation : Department wise WBS to be allowed for PO Creation

Question

Dear SAP PS Members
as per the SAP Standard anyone can choose the account assignment checked WBS for PR/PO Creation, however we are facing issues with this as end user may choose other department WBS out of understanding.which leads to reporting inconsistencies showing wrong picture of cost and assigned values.
is there any way by which we can allow each department to use only their department WBS for Procurement (materials and services).
that means SAP system shall control and avoid any transaction or postings on non relevant WBS's for the respective Department. ( other Dept. WBS)
please provide the ideas or workable logic ! 
Many Thanks
Avinash Shelke

Answer 1

How you are specifying that XXX-XX-X WBS is relevant to ABC department and so on? Are you using any custom field like 'Owner code' etc. to specify it?
Through std. customizing its not possible but through development it can be done as follows:
If you are maintaining department/owner code field n project structure for wbs then use this department-WBS field combination to validate it during PO, you need to maintain 'Department' field as a mandatory field in PO master (check whether it's custom field or std. in PO,i think it would be a custom one).
Once department field appears in PO that validate it from 'department-WBS' combination of project structure (use these fields from table PRPS) and pop-up warning/error message accordingly. You would require stand. user-exit for it in PO search for it in MM forum.
And if, you are not maintaining department/owner code field in WBS master then maintain it in a separate table (WBS->department) and validate in the same way as explained above.
Thanks.