Gravel is not the best option for your dog’s run as it can be harsh on your dog’s feet. The gravel can heat up in summer and burn your dog’s paws, and there can be sharp stones that can cut their feet too. If your dogs like to chew on rocks, then using gravel for your dog run could lead to dental damage, which could cost a lot to fix. If you want to use stone in your dog's run, choose a light-colored river stone. These rocks are soft and don't absorb heat too quickly.