Execute access on functions

I want to control access (update, delete) to my tables and have done that
with other DBMSs using stored procedures. Besides performance, I believe
that's one of the primary advantages of stored procedures. I grant execute
on the procedure to a group containing the users with controlled update
access. Never on the table. I cannot seem to find the equivalent in
postgres. I had hoped to be able to do this with user-defined functions
but the following statement implies that if the SECURITY DEFINER is used,
that *anyone* who can get to that function can execute it. Hardly the
solution I am looking for. The alternative being that I must grant update
to the table :(

The CREATE FUNCTION clause SECURITY DEFINER makes the function run with the
privileges of the user who created it. Otherwise, the INVOKER's privileges
are used.

Am I missing something here? Is there another way?
Thanks,
Kathy

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Kathryn K Smith
Los Alamos National Laboratory
505-699-9330
505-665-0505

The gentlest thing in the world overcomes the hardest thing in the
world. --Tao Te Ching