From IRS Publication 547: Loss of property due to damage by a family pet is not deductible as a casualty loss unless the requirements discussed earlier under Casualty are met. Example: Your antique oriental rug was damaged by your new puppy before it was housebroken. Because the damage was not unexpected and unusual, the loss is not deductible as a casualty loss.
[Rats. There goes my tax evasion scheme!]