<human>: I got Ryder last August(2014) when he was 3 months old from a local shelter. All they told us was that he was abused and was found covered in fleas/ticks. When we took him home he was extremely shy and took 3 days to finally warm up to me and my girlfriend. Whenever new people would come around he would be shy and hide for a while. 

He is now full grown, 45 lbs golden collie mix, Up until the past 2 months he would essentially just hide in our room when new people come over and slowly come out to greet them. Now, he barks at newcomers incessantly even if they offer him treats, sit on the ground, and talk to him in a soft voice. He views anyone who walks into our house as an extreme threat to him (Hair standing up on his back and keeping his distance). We've taken him to the dog park and taken him to training lessons to try and help him get over this fear of people but it doesn't seem to be helping. He is NOT aggressive in either of these situations. I would not bring him into public if I thought he was going to endanger others. 

This past week is what has really worried me, If I try to pick up any fuzz from him while he's ripping apart a toy, he snips at me. The snip is somewhere between a playful bite and a "I want to hurt you bite". 
He also snipped at one of my friend's kids feet today. He has always been skittish of children but never shown any signs of aggression. 

I am starting a new obedience training class next week at a more qualified place than pets mark. I am hoping that being in a setting with people and dogs 1-2x a week will help him with his aggression. 

Short of locking him up when guests come over (I'd like this to be a last resort),What other steps can I do to help my dog be more at ease when new comers come into our home?

Provide a brief overview of the text.
<bot>: My dog is transitioning from being a shy dog, to being mildly aggressive. What can I do to help him work towards understanding that newcomers in our home are not a threat?