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Being able to reach treats immediately is important for training, so the dog learns which behavior is being rewarded. Traditionally, dogs are taught to walk on the left side, so keep the treats in a left pocket or waist pouch. Put a few small treats in your closed fist and walk along with your hand in front of the dog's nose. Every few seconds, pop a treat into your dog's mouth as you continue walking. If the dog runs forward or hangs back, stop and call the dog to you. Continue to call the dog back patiently, until it returns. When it does, tell it to sit, feed it a treat, and praise it. Continue your walk as before, feeding it treats as you do. If the dog starts walking ahead but hasn't lunged to the end of the leash yet, say "Easy." Say "Yes" and give a treat if it responds by turning around and coming back to you. If the dog pulls at the leash to eliminate or to sniff an object, stop and call it back. When it comes, praise it, say "Yes," and let it go where it wants to go. Follow it so the leash stays slack. When you start out, you might just walk up and down the block, so the dog doesn't stop paying attention. Each day, walk a little further. After at least a week of this, straighten up and keep your hand near your pocket of treats, around waist level. Every other step or so, take a treat from your pocket and lower it to the dog. If the dog can walk for several minutes without pulling on the leash, you can slowly increase the number of steps between treats. Try to reach one treat per minute within a couple weeks. Dogs have trouble understanding the purpose of punishment, which makes it an ineffective motivation technique. You should only use these techniques sparingly to discourage unusually bad behavior, not on every walk:  Never use these techniques with a choke, pinch, or prong collar, or a head halter. If the dog ignores your commands to slow down and return to you, stop talking and turn back the way you came, tugging at the leash gently. Praise the dog when it catches up to you, then turn around and resume the walk.
Keep treats in a pouch or pocket. Feed the dog treats as you walk. Stop and call the dog if it moves away. Grant permission to investigate objects. Gradually increase the duration of the walks. Reduce the number of treats. Use punishment sparingly.