Reddit mentions of Cajun Pet Supply Reflective - Double Dog Leash - No Tangle - Two Dog Leash Coupler, Double Dog Walker and Trainer Leash - 2 Dogs Adjustable Splitter Lead 1" X 13-24" - Made in USA

Im sure you already read all about them but Gentle Leaders are fantastic for leash training a dog. They don't act like a muzzle so the dog can still eat, drink, bark, ect while wearing them but they provide just enough pressure on the muzzle when they pull that the dog quickly learns not to pull while on a leash.

I adopted both of my dogs at the ages of 1 and 2, so they were full grown and already strong as hell (boxer/bullmastiff mixes are super strong for their size), and the gentle leader was a key tool I used to help them learn leash manners.

They hated them at first and spent the first 5 minutes trying to paw it off their muzzle but they quickly got used to wearing it and after 2 weeks completely stopped pulling while they were on a leash.

I no longer use the gentle leader and instead use this harness with the leash attached to both the harness and their collar. But I also keep 2 gentle leaders in our "emergency kit" along with an extra tandem leach attachment. The emergency kit is a kit I have put together in case something crazy like a fire or tornado happens and I need to be able to control them both at the same time when things are going crazy around us. It also includes extra meds for the one dog on a daily medication as well as enough food for 3 days.