From 11g onward you can make a table read only

SQL> select owner,table_name,STATUS,READ_ONLY from dba_tables where table_name='DBACLASS';

OWNER                          TABLE_NAME                     STATUS   READ_ONLY
------------------------------ ------------------------------ -------- ---------
TEST                           DBACLASS                       VALID    NO

SQL> alter table test.dbaclass read only;

Table altered.

SQL>

SQL>  select owner,table_name,STATUS,READ_ONLY from dba_tables where table_name='DBACLASS';

OWNER                          TABLE_NAME                     STATUS   READ_ONLY
------------------------------ ------------------------------ -------- --------
TEST                           DBACLASS                       VALID    YES

Now if you try to insert or update anything, it will throw error.

SQL> conn test/test;
Connected.
SQL> insert into dbaclass  values ( 1);
insert into dbaclass  values ( 1)
            *
ERROR at line 1:
ORA-12081: update operation not allowed on table "TEST"."DBACLASS"

You can revert the changes and make it read write

SQL> alter table dbaclass read write;

Table altered.

SQL> insert into dbaclass  values ( 1);

1 row created.