Need some advice on training my 13 month old Golden

Question
My golden has always been a little on the hyper side, especially now that he has ..."matured"... shall we say. I have been living for the past 5 years in another country and bought him there, but this past month he went through the hassel of the plane travel and moving and now I am living with my grandparents while I look for a house, and this area is NOT dog friendly. I have had to board him, thinking I would have a house soon, but I haven't had all that much luck. He's at a place where I go every day to walk him and play with him, but I have noticed he has gotten a little aggressive with the other dogs...such as growling and showing his teeth. He has NEVER displayed that type of behavior before. Hardly ever barked, and if he did, it was for a reason. He has become nearly impossible to walk, without pulling my arm almost off. I am doing my best to control him, trying to get him to walk instead of lunge and pull and jump. But it's VERY difficult as he is a large dog. He used to sit, and was very trained... What can I do to calm him down? I'm thinking that if I get him fixed it might help some with his hyperness, but the aggressiveness towards the other dogs worries me. He has never (and still doesn't) shown anything like that to me personally or my family or friends. Just with other dogs, with us he's completely fine as far as his attitude goes....what can I do? Someone suggested training classes, but I'm afraid he'll be impossible to control while I'm there, or that he'll even get in a fight with the other dogs... Could he be showing this attitude as a sort of "rebelling" to being away from me? Or from all the trauma and stress of the past month? Any suggestions, training tips, or advice on how to help him..and ME?

Answer
Part of the problem likely is the lack of time you are spending on him.  You have turned his world upside down, and now he is alone much more of the time.  Neuter him if not already.  Obedience train him.  The key to most behavior problems is approaching things using the dog's natural instincts.  Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm  Talk to the instructor ahead of time.  The instructor should have experience with difficult dogs that need obedience training.  

A head collar may be the solution to the lunging on leash.  The leading brands are Promise,  Haltie, and Gentle Leader.  They have a strap going around the dogs nose looking something like a muzzle.  They work by pulling the dogs head around.  No other way gives you such great control with so little force.  The prong collar is now a dangerous relic of value only for its macho looks.  Do not consider using one without hands on instruction from somebody with plenty of experience with them.  Many obedience trainers still insist on using them.  You will have to work with the instructor even I disagree with his methods.