Why does my dog bark at random people?

Hi I am new to this site and to having a Staffie for many years. We 'rescued' Tyson form a relative who fed him rubbish, rarely walked him and he had no rules , just jumped all over the furniture and was basically left to do his own thing. There were always lots of people there and his owner described him to me as 'boisterous'. We have had him two weeks now and have gradually changed his food to Arden Grange (as recommended) which seems to have calmed him down, and our home is a calm environment and he seems generally very happy, he is getting lots of cuddles and had settled in well. He has about three hours walk (by which I mean runs) along the beach areas a day. He was fine at first greeting other dogs well even if they growled at him. I work from home and when customers come I have to put him in the kitchen or garden as he will jump up them and is distracting. I always give him a little treat and say ' good boy' when I let him back out. He sleeps in the kitchen with the door closed at night otherwise he will bark all night at every passing car or person if he has access to the lounge, so he is used to it and is quite happy with it then. Just recently he has started growling at me if I try to get him in the kitchen during the day, and it is aggressive. He has never been allowed on the furniture and at first he would comply if you said 'Down'. Now he has started ignoring that and it takes several attempts to get him to respond. He has also now stopped coming back when I call him when he is off the lead. I don't want to have to stop letting him run wild because I have to chase him. He was running after another dog on the beach and his owner was trying to get Tyson away from his dog. My husband got hold of Tys harness and was talking to him saying come on Ty and he turned his head and gave my husband a warning nip so that he let go and Ty could chase after the dog. The last few days when we have been out walking he has started growling at random dogs, who have not taken any interest in him on passing. We can walk past thirty dogs and then one particular one, even on the other side of the road, he will go mad barking and pulling in a very aggressive way. He has now taken to doing this with humans too. There is no rhyme or reason to it, just randomly takes offence to someone walking past or even just standing still as we walk past. It has happened with a group of Disabled people standing at a bus stop, an old lady with a walking stick (which I thought the stick may have disturbed him), numerous people who are just walking past and I am really beginning to worry. I am worried that he is confident now and this is his 'true' personality coming out? I thought maybe it is because he has never had guidelines and now he has that he has started growling about going in the kitchen but why the random aggression towards people who are innocently passing? There does not seem to be any reason, they could not be a threat, because they can be yards away or even the other side of the road? He has not been castrated and he is approx. 2 and a half years old. I know this is his teenage tantrum years and some people think that getting him done may improve this but on the RSPCA site it says that it should be done prior to aggressive behaviour and if that behaviour is already learned then it may not stop it? Help.... I want to be able to walk him with confidence that he will not show this behaviour. I don't want that 'look' you get as a Staffy owner that says keep that vicious animal away from me, but that is the impression that he is giving. He is a beautiful loving gentle dog. Any advice please?   

Hiya from me and Vin, sorry have no experience in this but there will be someone along who will be able to help x

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Hi and Welcome to the Forum from Flo and Me   

I don't have any real experience of this other than the odd occurance when my Flo takes a dislike to another dog at 100yds for no apparent reason   

Like you say, it is teenage behaviour and you might well need to go back to basics to reinforce good behaviour.

We do have more experienced people within the Forum who will be pleased to offer further advice i'm sure.

Welcome from me and Alfie.
Others more experienced will be on later. Rachel is very good with dog training/behaviour.

hia from me and sasha   ,i'm sure when Rach comes along in a bit she will be able to help.

Hi and welcome from me and Daisy   

Hi and welcome from me and my two

Welcome from the kids and I

Welcome from Darcy and me

Hi and welcome to the forum from Rocky and me.

Try posting in the Training & Behaviour section outlining your issues, it may well get overlooked in here.

Hello and welcome I think he's testing his new boundaries and seeing what he can get away with.. A mix of this and hormones plus new environment he's probably a bit all over the place! Keep consistent with the commands and rules and up his obedience training and positive socialization. Does he show aggression to anyone in a controlled setting (visitors/people he knows) or is it just people passing his territory?

Hi and welcome to the forum from me and the zoo xx