My Chihuahuas wear a coat only if it's below about 17-20 degrees F. But anyway, their coat has a little slit up near the collar area, a little in front of the withers, where you can run the leash through. I put the harness on and then the coat over the top of that if I have to take them on a leash walk. Usually it's off leash around here. And if it gets much colder than that, we skip the walks. lol.