"Locking rows"

I have a customer requirement/desire. The system is (among other things)
essentially a employee time sheet. The manager wants for an employee to not
be able to modify a given row in the table they enter time into once it is
committed. I personally see issues with this, but I am willing to try to give
him what he wants. If it creates issues we can sort them out, once he sees
the issues.

The only way I see to do this is to add a column (call it lock). I will
then set this up as a default entry with a value of TRUE. The form the
employee uses to enter this will, of course, not display this column. The
I will create a function that on UPDATE, checks for the presence of the 1 in
this row, and rejects the update. Then I will give the manager a form where
he can set this flag to FALSE.

Looks ugly, and convulsed to me.

Is here a more "database native" way to handle this?

--
"They that would give up essential liberty for temporary safety deserve
neither liberty nor safety."
-- Benjamin Franklin