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, replied 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 received another letter from his wife, "Dear Husband, You wouldn't believe what happened, some men came with  shovels to the house, and dug up all the back garden."

The prisoner wrote another letter back, "Dear wife, now is the best time to plant the lettuce."