The most important thing to consider is your dog’s size and strength and how that will affect your walks. A bigger dog who likes to bolt may snap a lighter leash, while a smaller, low-energy dog may be overwhelmed by the weight of a thicker leash. Additionally, dogs who chew on their leash will need leashes made out of durable materials. Consider metal chain leashes, and definitely avoid leather. Dogs who are prone to dirtying a leash will need one that is easily washable. Consider a nylon leash, which won’t hold bad smells like leather.