Your Dog Needs Dog Training Leads
Leashes are the more common name for dog training leads. Some dog trainers and pet stores prefer the term "dog training leads", so if they say it, you know what they are talking about. In most places in the United States and England, you MUST have some sort of dog training lead on your dog every time the dog is outside of your fenced in property. You can get severely fined for breaking leash laws and risk having your dog impounded.
No Need To Stress
As far as cost goes, dog training leads or leashes are among the cheapest pieces of equipment you'll ever buy. For legal purposes, even rope tied to the dog's collar would count as a lead. But a rope should only be used in emergencies. They are incredibly undependable. A dog training lead with a metal clip that solidly clips onto the dog's collar is far more reliable.
There are many various dog training leads in colors, materials and lengths. The most usual is a six foot lead. This is short enough to control even a large dog. If you want the dog to roam some, but still keep in contact with the dog, consider getting a twelve foot or even twenty four foot dog training lead. Lunge leads made for horses will also work for large dogs.
Why Such A Long Lead?
In training, you want to teach your dog to come back to you when called, but keep within your area's leash laws. A very long lead allows the dog to wander off a bit for a sniff, and then learns to come back to you when you call (whether the dog comes to you voluntarily or is hauled in while heaped with praise). A six foot lead does not work as well teaching some commands like retrieve or come back to you when called. The dog looks at you as if to say, "Heck, I'm only a couple of feet away. Quit your whistling."
Another reason for such long dog training leads are for the incredibly advanced training of tracking dogs (dogs that follow a specific scent trail or trained to find a specific odor). When on the hunt for a certain smell, the dog will disappear among places really hard for you to follow. In this way, you still have contact with an invaluable dog. There is also a competitive dog sport called tracking where a dog follows a hidden pre-laid trail. The fifty foot lead is essential in these courses.