“Sly as a fox" has been a traditional saying for hundreds of years. It means that someone is particularly crafty or tricky. If you're as sly as a fox, you are experienced and cunning and can usually get whatever you want, sometimes by underhanded means. Long ago, fables, such as Aesop's The Fox and the Crow, portrayed the fox as a creature that was very crafty and cunning as a hunter. Although there are plenty of other animals that are cunning hunters, the fox became associated with trickery. I hope this helps!
