He has also started to be aggressive towards other dogs. What can you advise to overcome these problems?
Mark Whitehouse says: Any dog that is unruly is also a dog that is out of control and you should look back at your foundation training to see where you have gone wrong.
You might need to re-install some of those basics such as sit and stay, walk at heel and re-install the stop whistle back into the dog’s memory.
All of these commands are controlling exercises for your dog and play a very important role when out in the working field when the pressure is likely to build up.
The aggression towards other dogs can be a two-part problem in my experience.
The first part is that some dogs are very protective towards their owners and if other dogs encroach into that comfort zone they can be quite aggressive towards them.
The second one is that dogs that have had very little socialising can be frightened or feel threatened when approached by other dogs and snap out to protect themselves.
My advice to help solve both problems is to join a local group training class and pend lots of time socialising your dog with all different breeds and types of dogs as often as possible.
The more time you can spend working your dog alongside others the more she will become a team player.