>>Have you tried using a Default on the column in SQL Server?
>
>I am using default = getdate() for the column but that only work at INSERT but not UPDATE.

You can use

--drop table test
--create table test (id int identity, date Datetime default getdate())
--insert test values (default)
update test set date=default where id=1
select * from test

if you are passing the sql statement to the back end. I don't know how to make ADO.NET generate this command. Does anybody know?

Triggers, as Bonnie mentioned, are probably a better solution, although they create their own problems.