@Scrbblchick -- I do the same thing with my rent, pretty much for the same reason: my landlord would hang on to the check for three weeks. Not fun.
I save the receipt and also take a picture of the filled out money order before I take it to his office. If his secretary is there, I *always* get a receipt, because he's so scatterbrained, he's told me I didn't pay the rent when I did! I had the receipt to show him. Once, I had to show him the picture on my phone to satisfy him. It was insane.
He has to keep up with a money order, though, if he wants the rent money. I don't feel a bit bad about asking for a receipt or taking a picture of the money order if he's going to be so airheaded about my money.