To make an appropriate tail for your miniature dog, take some of your roving fiber and roll it into a cylinder the correct thickness for an appropriate tail. Don't worry about the tail being too long, you will need extra fiber on the end to felt the tail to the dog's body. Needlefelt the tail to the correct shape. If your dog has a tail with long fur carried upright above its body, felt the tail to the correct shape and length for the fur support, and lightly felt longer fibers into the main shape to create the long haired tail. If your dog has a thin rope of a tail, needlefelt a very thin tail, adding long fibers to the end if the dog's tail is trimmed so that the skin is visible before an end pouffe. Luckily my Jack Russell has a docked round tail, a bit like a handle, so I needed a short sausage of felted roving in black for my dog's tail.
The small roll of fibers beside the dog's back legs is the same size as I used to start felting my black tail. I am showing you a group of white fibers because they photograph better against the foam felting pad.
When you have shaped your tail to the correct stiffness and shape, use your felting needle to join the tail to the body by felting through the loose fibers at the end of the tail. If your fibers are too long, trim them to a better length for attaching the tail.
Be careful how you needle felt the tail to the body if your tail is a different color from the body, the fibers can blend and form a patch. To make a clean join, work your needle carefully up and down around the base of the tail.