Here is a testimonial how backing up a harness saved Hugo's life.

Every day dogs get out of their collars and harnesses, or they break at the worst time. Just like wearing a seat belt when driving a car, we want to back up our dogs collars and harnesses for safety reasons.A simple back up can save your dog's life as you can see in the testimonial video about how a back-up saved Hugo's life.

Below are examples of training collars and a harness with back ups. Attach a second collar with tags to their walking collar or harness with a simple carabiner. Keep your dogs safe: back up their collar or harness.

Martingale

When backing up your martingale attach it to the side buckle not the same O ring the leash attaches to so the collar can move freely.

Pinch/Prong Collar

When backing up your Pinch/Prong collar to attach it to the "Dead Ring" not the same rotating O ring the leash attaches to so the collar can move freely.

Starmark Collar

When backing up your Starmark collar to attach it to the side whole not the same O ring the leash attaches to so the collar can move freely. The Starmark collar also comes with a slip back up you can use instead.

Easy Walk Harness

When backing up your Easy Walk Harness, or any other harness attach it to anything but the same rotating O ring the leash attaches to so the collar can move freely.

We are using a basic carabiner in these examples as they are easily accessible to everyone.

Dog Collar Safety Clips on Amazon

Best Pet Supplies Voyager Dog Collar Safety Clip with Dual Clasps, Collars and No Pull Harness Connectors, Training for Walking, Running, and Hiking, Safety Clip - Black
Hs Herm. Sprenger Prong Collar Safety Clip (Black) with Reflective Stripes 6"-8" Pack of 1 Dog Leash Safety Strap - Enhanced Durability for Secure Leash Connection - Ideal for Safe Walk and Training
PetBonus Dog Collar Safety Clip, Waterproof Backup Safety Strap for Dog Harness to Prong Collar, Odor Proof Double Ended Clasp Leash Connector for Training Walking (Black

We also recommend and use other forms of backups. I use a Biothane Saftey clip from What a Cutie, a NYC company and members of the Canine Cohen Club.