Salesperson/Purchaser Code (Table 13) Nav 2009 R2)

Hi,

We are having a lot of salespersons names in this table and since i have joined this company in 2011 to till now there are almost 60 to 70 names being used for those people who joined as salesman and left the company. Most of the names are quite common and we have salesman codes created as JT1, JT2 or GS1 and GS2 and etc

My question is how can we block the operations dept from not using these salesman code who has already left the company and there names are no more used while creating sales orders. The best option is to have a block field in this table with a check mark under the salesman code.

How to implement or write a code to do it. Can someone tell me how to do it in a simple steps so that i can try first in our test database and when successful I can implement the same in live database.

I want the salesman code to be blocked from being used in sales quotes and sales orders. If I can get simple steps I can do it on my own as our vendor is charging us to do it and if I get simple steps I can do it.

Pls Help

Regards
Khan