It's beyond me why EVERY dog owner doesn't use these when they're walking their dogs, on leash or off leash, on city streets or mountain trails. "Outward Hound" is the maker of this ultra-affordable piece of dog clothing. You can find their stuff at http://www.kingwholesale.com/ (for the best prices). You might check local retailers too.
The vest goes on in a jiffy with velcro at the collar and belly strap. It dries in a flash. It will increase your dog's visibility day AND night. Lizzie goes with me on daily horse outings now, and this vest makes her more visible to ME if she starts to detour too far away.
You could pay a lot more for something fancier, but I've loved these Outward Hound bargains for years.