The photo above shows three different types of pet memorial rocks. The 3 cats on the top rock shows mainly the faces, with only part of the bodies painted. This style is used mainly for multiple pets on a rock. The rock on the left is done in 2-D fashion. It's a picture of a pet on a rock. The rock on the right is a pet done in 3-D, where the whole pet takes on the whole shape of the rock.
Any painted rock can be a pet memorial rock. Add a message, name or birth/death dates to the top of the rock, If you want the message to show, If you don't want the message to show, add it to the bottom/underneath the rock.
The rocks on the following pages will help give you ideas of what can be done as far as messages, 2-D rocks and adding collars and tags. These are not all memorial rocks, many of the pets are living. This will just give you an idea of how a collar and tag might look on your rock.