Locking production PL/SQL stored procedures

Hi,

     do you know any way to lock PL/SQL packages?
     I have a production environment on user PROD, and I'm developing
     next release of the application on user DEV. But I'm afraid I could
     connect by mistake to PROD, and spoil the system that is on
     production.
     I tried revoking the grant RESOURCE to PROD (it contains
     CREATE PROCEDURE). Then, I cannot create new procedures, but I
     still can 'CREATE or REPLACE' or DROP packages.
          Any suggestion?

     Thanks,
          I'll apreciate aan email to dpinol_at_cesca.es