Paying your rent
If you pay your rent on a weekly basis, by law, your landlord should provide you with a rent book.
If you do not pay your rent on a weekly basis, still ask your landlord to provide a rent book or, failing this, ask for a receipt each time you pay your rent.
Either way, this will provide a correct record of payments, especially if you pay your rent in cash.
Payments and receipts
If you are unhappy about paying rent in cash, pay by cheque instead - make sure you still get receipts or your rent book is kept up-to-date.
If you have a written agreement, this should state how much rent you should pay each month/week and the due date.