Add timestamp to field automatically in PostgreSQL
You could use a trigger like this:

CREATE FUNCTION last_upd_trig() RETURNS trigger
   LANGUAGE plpgsql AS
$$BEGIN
   NEW.lastupdate := current_timestamp;
   RETURN NEW;
END;$$;

CREATE TRIGGER last_upd_trigger
   BEFORE INSERT OR UPDATE ON finds
   FOR EACH ROW
   EXECUTE PROCEDURE last_upd_trig();