Hi, i can imagine your dog wants to explore, he is nosy and wants to get around. If you want to do that without a lead I suggest you train with your dog inside the kennel if it is big enoug. Have him walk by your side in the kennel and praise him whenever he does well, give him treats. He must realise that it is good for him to stay by your side an not leave you as long as you tell him so.
I hope i could help a little. Of course this takes a while, please do not be frustrated if the change needs its time.
All the best and nice greetings from Vienna,
Michael