How to restrict the fields in Zoho Books without validation rule?

How to restrict the fields in Zoho Books without validation rule?

Hello Team,

        
In Item modules we have two fields 1.Package in Count ,2.Package in Kg. In this cases we need to restrict the user for they gives values for any one field .Package value will be in "Count" or "Kg". 

      Is this possible?

      We already tried with custom function if two values are filled function going to clear any one value.But we need to pass a instant alert for this flow.For Example "Gives any one value Package Kg or Package Count".

Thanks & Regards,
Thisai Moorthy.