Hi! Thanks for getting in touch.
If you missed the "window of opportunity" for socialising your puppy when they were still young, it's not a surprise that they have some behavioural issues today. The answer to your problem is to still socialise your pup - but it will take a lot more time and patience than it would have if they were younger.
Take them to as many different places, and have them meet as many people and other dogs as possible. Nothing too overwhelming (e.g. crowds, dog parks, etc). You can choose more "challenging" environments once your dog builds their confidence. Always reward good behaviour with treats and praise.
If your dog has certain triggers (e.g. other dogs), you'll have to work on desensitizing them. For this, you'll have to expose them to their trigger at a distance and at a low intensity. Always pair the trigger with something positive (like lots of treats!). Ignore bad behaviour and remove them from the trigger if they become overwhelmed.
Working on training alongside socialisation and desensitization helps to give your dog structure and keeps them mentally stimulated. Also ensure they're getting the proper amount of exercise. Dogs that are under-stimulated tend to respond to triggers more aggressively than others.
Remember, this will take time. Don't give up! And if you need professional help, don't hesitate to get in touch with an animal behaviourist.
Best of luck!
Justine Seraphin, BSc (Hons) Animal Behaviour and Welfare
