My dog just got in from her evening walk,all things seemingly normal. She then came into the livingroom and peed right in the middle of a rug. She is 2 years old and an italian greyhound. I thought she knew better than this ,especially since she had just been out. there have been no strange animals in the house and nothing odd happened today. What would cause a fixed female dog who is house trained to do this? She does this about every other month-Could she just be not very smart?