PROCEDURE Block_Show_Only(P_BlockNaam Varchar2) IS
  v_BlockID Block;
  no_block exception;
BEGIN
   v_BlockID := Find_Block( P_BlockNaam);
   if id_Null( v_BlockID) then
     raise no_block;
   end if;  
   -- watching only now possible
   set_block_property( v_BlockID , Query_allowed, property_false);
   set_block_property( v_BlockID , Delete_Allowed,property_false);
   set_block_property( v_BlockID , Update_Allowed,property_false);  
   set_block_property( v_BlockID , Insert_Allowed,property_false);    
EXCEPTION
   when no_block then
     Your error code;
END;