Option to disable rate field in Zoho books purchase Order

Is there any feature to disable the option for rate editing in Purchase Orders? Because the purchase executive can edit the price/rate and that can be an issue. We need to verify the POs again and again and there needs to be a person to monitor the rates and that defeats the purpose of having software.

There should be an option to disable the rate editing option or to enable or disable the option in the role module.