Dog ears are basically skin pleats.
Dog ears are created when a portion of tissue is removed like in a tummy tuck and there is excess which bunches up at the edges of the incision. Dog ears can be prevented by extending the incision farther to remove the excess skin. The trade off is a longer scar. Usually dog ears can be prevented with proper planning but sometimes they cannot, but are easily fixed. Please check out some before and after photos in the link below for some examples of tummy tuck results.