(...)
We have just started 1:1 dog training with a professional who has also noticed his resource guarding and growling/snapping.
My Vet is saying that it’s a good idea that we’re training him before he grows bigger (for obvious reasons), and now I’m becoming quite anxious that our puppy has some kind of genetic / in-built aggression that is going to be a real issue. Originally I thought ‘oh this just a normal puppy’, but I’m genuinely worried that we have a real behavioural problem.
Do any of you have similar experiences and tips for how we ‘train’ out the aggression? We chose this breed specifically because of their temperament so I’m a little taken aback that this is the main issue for us.
First: you're not going to resolve your specific problem with advice from the Internet. It's important to work with a good trainer, someone who will teach you how to read your dog's personality and behaviour. I would also suggest enrolling in a group obedience class at a good school that uses positive methods. There's a lot of learning to be gained from group classes, not only from the instructor but also from the other participants, and it's important for dogs to learn to function in different contexts with distractions.
Having said that, while you're not going to resolve the problem on the Internet, the Internet is a good place to get information that might help you to understand where the problem comes from. As Prism pointed out, some behavioural issues can stem from how the pups were raised by the breeder. If the pups weren't properly handled or exposed to different environmental elements, this would make a difference, as would the choice of pup for each owner. Most good breeders select the pups for buyers because they are best-placed to know each individual pup's temperament. As Prism noted, a good breeder would not (for example) place a shy puppy in an inexperienced home. If, on the other hand, you chose your own pup from the litter, maybe you could think back to why you chose him. What did he do that made you think he was the right pup for you? This would give you some insight into his personality. As Prism also pointed out, innate aggression is extremely rare in Goldens. The likelihood that you got an "aggressive" puppy is very small indeed.
The reality is that an awful lot depends on what you do with the pup in the early weeks after you bring him home. The period from two to four months is extremely important for socialization. This does not only mean playing with other dogs. It also (and mainly) means introducing the pup to the world in which he will live: taking him out and about, showing him new places, introducing him to new people, sounds, sights, smells and surfaces. Handling him extensively, clipping his nails, cleaning his ears, brushing him, lifting him on and off tables or furniture, teaching him the basic commands, getting him used to being handled by different people.
If you didn't do this with him, then that may well be at least part of the reason why he reacted as he did at the vet's. He would have been frightened because he had never been exposed to anything like that before.
The other thing I would say is that IMHO many if not most problems of this type are caused by what humans do with dogs, and not from an innate behavioural issue in the dog. Aggressive puppies are rare, but puppies with fear issues or resource guarding issues (i.e. pups that react defensively) are more common because in many cases they haven't been given the tools they need to function in the human world. They are stressed because they don't know what's expected of them.
If this were my pup, I'd start by having his personality assessed. Is he shy, fearful or wary? Is he bossy? Etc. I'd do all the things on Gdgli's list. And then I would work on developing his confidence, through formal training in a group setting. A dog who knows what's expected of him and how to behave in specific circumstances is less likely to react defensively. I'd take him out and about, making sure not to overface him and not to force him into situations where he's uncomfortable. And so on. Very rarely, with 4-month-old puppies, will it be a case of "training out aggression". It's more a case of forming a relationship in which the dog is comfortable and confident and able to function well.
Best of luck! Let us know how things go.