DataSource Controls :: Generate A Unique Ref Number And Insert Into The Database

I am generating a unique Ref number using this sql statement: SELECT REPLACE(STR(CAST(CAST(NEWID() AS binary(5)) AS bigint),12),0,0) as REF Subsequently, I need to insert this REF into sql database table in stored procedure. Here is what I did in my stored procedure:

USE [iBankRecords]
GO
/****** Object: StoredProcedure [dbo].[stp_addPayee] Script Date: 07/05/2010 21:57:07 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROC [dbo].[stp_addPayee]
(
@CUSTID char(10),
@PAYEEACCNUM nvarchar(20),
@PAYEEACCTYPE char(10) ,
@PAYEENAME char(20),
@PAYERINITIAL char(20),
)
AS
DECLARE
@ReturnValue int
INSERT INTO PAYEE (CUSTID, PAYEEACCNUM,PAYEEACCTYPE,PAYEENAME,PAYERINITIAL, REF)
VALUES (@CUSTID,@PAYEEACCNUM,@PAYEEACCTYPE,@PAYEENAME,@PAYERINITIAL, REF)
IF @@ERROR<>0
BEGIN
PRINT 'ERROR'
SET @ReturnValue=1
RETURN @RETURNVALUE
END
ELSE
BEGIN
SET @ReturnValue=0
RETURN @RETURNVALUE
END

May I know how do I have generating a unique ref num and inserting the REF into the above statement?