Immutable attributes?

Hello,

I have a table like this:

create table test (
"test_id" serial primary key,
"created" timestamp with time zone
default current_timestamp
check(created = current_timestamp),
"some_datum" int not null
);

My question concerns the "created" attribute: I want this to reflect when
the tuple was craeated; and I want to make sure that the timestamp is not
wrong. That will work with the above schema. However, I also want to make
sure that the "crated" attribut for a tuple is not changed once it has
been set.

I'm thinking about implementing it through a trigger, but is there a
better way to create such "immutable" attributes?

/Troels