Dog-walkers, pet-sitters, and groomers can use this resignation letter as final notice to the animal's owners.
{Your address}
{City, State, Zip}
{Date}
{Recipient}
{Address}
{City, State, Zip}
Dear {Name},
Effective immediately, I will no longer be able to care for your {dog/cat/etc.}. I am leaving the pet sitting business entirely, so this is not a reflection on the behavior of your pets in particular. In fact, I've enjoyed my time hanging with {pets' names}, and I will miss them when I go.
If you're interested, I do have the names of several other pet sitters in your area, all of whom I totally recommend.
Sincerely,
{Name}