If your dog gets overheated easily during walks, you can make a cooling storage vest from an old pair of cotton cargo pants. Once sewn together, all you need to do is dip the vest in water and put it on your dog -- your pet will experience evaporative cooling as the vest dries.
Instructables user obake shares this vest design or dogs prone to overheating outside. You can also put ice or ice packs in the pockets for additional cooling.
You'll need to cut the inseam out of an old pair of cargo pants, and then cut and sew the remaining pieces together to make the vest. Full instructions and step-by-step photos can be found at the Instructables link below.
Doggy Cooling Vest/Backpack (from cargo pants) [Instructables]