You can call user-defined function as a DELETE Trigger from table definition window. If your null codes are hardcoded, you can simply put a check with

IF code = 'C000000'
RETURN .F.
ENDIF

Bye
Jayesh

>I frequently use a set of what I used to call null records, before we had null values, as relation templates in a set of related tables. For example a customer with key C00000, name {new customer}, etc.
>
>Any suggestions on using some triggers to prevent their deletion, or properties to prevent their display?
>
>TIA,
>Al Allison, [AMPS Automation, Inc.]