Once I itemized the features of dog harnesses I realized the recklessness of not describing leash options first. So here I try to make up for the oversight.
There are many purposes served by the dog leash. While a leash seems simple, there are many options you probably don't even know about. From reflective material (even lights!) to sound emitting attachments that make your leash an electronic training device. But the basics matter.
The first decision to make is how long the leash should be. Long enough to reach the dog, obviously, but consider the work you'll do. If you need to work at a distance you'll need more length. If you have a tall dog, all that extra leash just gets in the way. If you work hands free, you'll need a connector for your belt. Your dog's size decides weight of the leash and it's hardware. And your personal preferences, the material from which and by whom it is made.
I prefer a 6' leather leash with a boat clip and detachable handle that I can use for a traffic lead. Already, I see I've lost you. As the Imelda Marcos of leashes, I can help.