Hi Cody and Dogcharacter,
Thank you for your comfort and suggestion. I am becoming to be very anxious that my dog wun walk on a leash.
I am not sure if my dog is afriad of anything that is out there or not. When he was 3 months old, I started to bring him to my mum's house to play with my other dog. He will get pretty excited. Even when he is at home with me, he gets excited very easily too. He started to wear the collar 24hours round since the day I brought him home from the pet shop. I never use the leash to punish him. Though he is active and excited when indoor, he become afriad when I bring him out and put him on the floor, whether is it grass patch or void deck. He will be very alert and fearful of his surrounding. I dunno what cause that fear. At first, I thought he might be fearful cos he is not used to it. So, then I tried to train him to walk with a leash. I only train him on leash at home. Once, he is on a leash, his tail is down towards the floor, and he wun move. Not at all. Even when I drag and pull, he will not walk.
Now, I am beginning to wonder did the petshop use the leash or something similar to punish the dog before I bought him. Can anyone help me?