Hugo a few things could help leaving the dog chained up most of the time in your yard so he can't go and hide go about your business ignoring the dog mostly at first farther away from people then closer to people walking by he will eventually not be scared and may come out barking at people going by he will think he is scaring them away. When he shows that he is becoming desisted to people on the chain have someone play hide & seek with the dog have them look over the fence or around a corner as soon as the dog even looks at them have them run off like he is the scariest dog they have ever scene if done right he might look that way someday do it a few times then stop soon he should be barking at them. Also I'd start hand feeding and using treats for obedience which should be done often, work on the sit stay in public slowly doing it closer to people and crowds and you being farther away from the dog to the point you leave him alone for 15 minutes tied to something for everybody's safety. Being a kennel dog he may have not had much human contact in his first 12 weeks he may have missed the prime imprinting period he is maturing slowly he still may prove himself with a little help.