"Constant" fields in a table

Hi,

I want to tighten down my db schema as much as possible against accidential
corruption. For this, I'd like to have fields that can only inserted and
not later changed (think some sort of "id", account names, etc., which are
often not only stored in the database but also in external places so
changing is just a definitive DON'T).

Obviously I can check this with triggers, but it occured me that some kind
of "CONSTANT" field attribute would be nice. Perhaps such a construct
already exists? Or perhaps somebody has come up with a generic way to do
this without having to write 30 or 50 small triggers all over the place?

thanks in advance
cheers
-- vbi

(I read the list, but will be away on holidays later today, so don't worry
if you don't hear back from me. Your input is appreciated.)

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