I keep a full record of all postal and BACS payments received on a separate sheet.
I now also give a list of all cheques being deposited to the bank with the paying in book as there is never enough room on the back of the paying in slip (got 85 cheques to bank on Monday!)
Had a £21 cheque for window cleaning bounce on me last week, the lads had taken it at the door as payment when they were cleaning, no cheque guarantee number on the rear.
I now make sure that all cheques have at least the address on the rear just so I can follow them up.