Parameters from trigger to function.

Everyone, I need your help,

I am trying to pass a parameter to a function that is to be called by a
trigger.  But, the correct function isn't being recognized and I am getting
an error stating that the function doesn't exist even though it does!

What I got going in psql...

CREATE TABLE testing (id SERIAL, data text);  -- sequence = testing_id_seq

CREATE OR REPLACE FUNCTION id_protect(text) RETURNS TRIGGER AS '
        DECLARE
                sequence ALIAS FOR $1;
        BEGIN
                IF TG_OP = ''INSERT'' THEN
                        NEW.id := nextval(sequence);
                        RETURN NEW;
                ELSIF TG_OP = ''UPDATE'' THEN
                        NEW.id := OLD.id;
                        RETURN NEW;
                ELSE
                        RETURN NEW;
                END IF;
        END;
' LANGUAGE PLPGSQL;

\df id_protect
            List of Functions
 Result data type | Schema |    Name    | Argument data types
-------------------+----------+------------+------------------------
"trigger"             | public    | id_protect | text

CREATE TRIGGER protector BEFORE INSERT OR UPDATE ON testing FOR EACH ROW
EXECUTE PROCEDURE id_protect('testing_id_seq');

ERROR:  function id_protect() does not exist

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Now, why am I getting that error?

Thx all,
  Vams