There are various techniques to teach a dog to stay on a leash. Here are some tips:

1. Start with short walks: If your dog is not yet used to a leash, begin with short walks in the garden or a quiet park. If your dog pulls on the leash, stop and wait until he looks back at you. Reward him when he pays attention to you and stays by your side.
2. Use an appropriate leash and collar/harness: Choose a leash that is suitable for your dog's size and strength. The collar or harness should be comfortable and secure. A well-fitting harness can be more beneficial for dogs that tend to pull on the leash.
3. Use positive reinforcement: Reward your dog when he stays on the leash. Use treats or positive reinforcement, such as praise or petting, when your dog stays by your side.
4. Use the right command: Use a simple and clear command, such as "heel." Repeat the command if your dog pulls on the leash to remind him to stay with you.
5. Pay attention to body language: Your body language is important to signal to your dog that he should stay on the leash. Stand upright and relaxed and avoid pulling on the leash or acting anxious.
6. Train regularly: Practice regularly with your dog to ensure he stays on the leash. The more often you train, the faster your dog will learn to stay on the leash.

It is important to note that every dog is an individual and may react differently to various training methods. If you are having difficulty keeping your dog on a leash, consult a professional dog trainer for help.