Aggressive fur baby

Hi ploppy thanks for your post.
Inter-dog aggression is almost always a socialisation problem. It is unusual for this sort of thing to pop up suddenly in an older dog with a good history with other dogs but it can happen. It may that she has had a recent bad experience with a another dog or even just that your dog hasn't had alot of socialisation recently and has reverted to poor doggie communication skills.

The first thing to try therefore is resocialisation and lots of it! In the initial part of the training it is best to walk your girl regulalry on lead. I would suggest using a head collar for this training. These are sold under many brand names including halti and gentle leader but are basically all the same. The idea is that instead of the collar going around the neck the collar goes around the nose but also has a part that clips behind the ears to hold it on. The lead is attached to a ring that hangs under the nose and when the dog pulls the nose band tightens. This is no way hurts the dog it is just annoying for the dog like someone holding your nose. However the main idea of the design is that the dog is attached to the lead via its nose and head rather than its neck and shoulder area where its powerful muscles are. The dog cannot pull you using only its nose so you can assert full control over the dogs behaviour because the dog can only go where you let it go. Because the dog cannot pull you towards other dogs on walks it also learns to react more calmly to the situation and also to look to you for guidance as to how to react because you are in control of it. If you do decide to try the head collar it is important that you read the instructions that come with it in order for it to work properly especially the instructions on introducing your dog to the head collar as dogs may initially dislike having a band around their nose.

The head collar is a great socialisation tool. Take her for walks on it as often as you can, initially to areas with some dogs and later to areas with many dogs. Go for a normal walk and be calm, if you tense as another dog approaches your dog will interpret this to mean that you the pack leader also think another dog is a problem. As the dog gets closer you dog may attempt to growl and lunge. Make sure you are holding the leash vertically so the head collar can control her behavior. Ignore the bad behavior yourself but as soon as it stop praise her warmly. Trying to use treats in this situation is probably not appropriate as she may snap at your hand in her excitement over the other dog. Continue to praise calmness and ignore bad reactions. Walk calmy and firmly onwards and you dog will have to follow.

This should correct your dogs on leash aggression very quickly and should also make her much calmer around dogs at any time. When she does becomes less interested in other dogs you can start taking her to off leash areas with a muzzle on if neccessary and with toys or treats on you. Before letting her off leash let her see the toys or treats. Keep her interested in what you have as you walk around the park offleash. Practise the come command with the treats. After her large amount of on lead socialisation she should now find you and your treats much more exciting than other dogs and respond to the 'come' command that you give as soon as she starts looking towards other dogs.