Durability
Wolverine Wins
Dog
Domestic dog durability varies considerably by breed, with some specimens requiring constant veterinary intervention and others surviving well into their second decade with minimal maintenance. The species has, unfortunately, traded some physical robustness for aesthetic modifications of questionable utility. Flat-faced breeds struggle to breathe; elongated breeds develop spinal complications; miniaturised breeds shiver perpetually. The average mixed-breed dog, however, demonstrates reasonable durability under typical domestic conditions, provided those conditions exclude chocolate, grapes, and onions.
Wolverine
The wolverine has evolved durability as a core survival mechanism. Its skeletal structure withstands impacts that would hospitalise larger predators. Its metabolism allows sustained travel across fifty kilometres of frozen terrain daily. Its immune system apparently shrugs off infections that would prove fatal to other mustelids. Perhaps most remarkably, the wolverine's psychological durability remains unmatched. No documented evidence suggests a wolverine has ever experienced self-doubt, hesitation, or the sensation of being intimidated. This mental fortitude may represent its most durable characteristic.
VERDICT
Evolved specifically for survival in Earth's harshest environments with apparent immunity to discouragement.