A prisoner in jail receives a letter from his wife: Dear husband, I have decided to plant some lettuce in the back garden. When is the best time to plant them?
The prisoner, knowing that the prison guards read all mail, replies in a letter: Dear wife, whatever you do, do not touch the back garden. That is where I hid all the money.
A week or so later, he receives another letter from his wife. Dear husband, you wouldn't believe what happened. Some men came with shovels to the house and dug up the back garden.
The prisoner writes back: Dear wife, now is the best time to plant the lettuce.