Holding the leash behind your back can provide several benefits during dog training:

1. Clear Communication: By holding the leash behind your back, you can easily show the dog the exact position you want them to be in.

2. Preventing Forging: When dogs are in the heel position, they should walk calmly beside you without pulling or forging ahead (their ear should be between your hip bone and butt cheek). Holding the leash behind your back can discourage them from getting ahead and reinforce the concept of staying by your side.

3. Angle Control: If the dog attempts to forge or move ahead, holding the leash behind your back allows you to quickly cut the angle and apply a quick "pop pop-release" of leash pressure, when necessary. This will course correct the dog back to the right position and maintain control over their movements.

4. Prong Collar Application: If you use a prong collar as part of your training tools, holding the leash behind your back can make it easier to apply leash pressure with the collar. This can provide a clearer signal to the dog and make it easier to guide them back to the correct position.

Once your dog gets used to the new position you can then move to holding the leash in front of you.