Actually many dogs will show nails and often coyotes don't, this is not a reliable method. The pads of a coyotes paw are much smaller than a dogs relative to body size. Almost every domestic dogs paw is round with a large rear pad. Coyotes feet are oval shape and have a smaller rear pad, also unless the coyote is running or trotting they usually place the front and rear feet in the same print. Most experienced trappers can tell the difference easily, but many trappers will have a hard time distinguishing between a fox and a coyote track.