I'm so sorry for the delay. I didn't receive notice of the reply. I apologize profusely.
Much of dog communication is accomplished through body language. While you might not see any cause for Willie's behavior, it may be body language which is cueing his behavior. It could be the dog is a dominant dog and Willie feels challenged or the other dog might be sending signals of aggression that you didn't realize. So one thing to do is learn body language.
When you worry and shorten the leash that does telegraph your feelings. The dog doesn't know that you are worried about his reaction, he assumes it is the other dogs or people. So if possible keep the leash slack and relack.
Get Willie obedience trained. Obedience training does more than just teach a dog commands. It helps them build self confidence and overcome some fearfulness. It also establishes the humans as the boss or leader. As the boss or leader, it is your job to protect him rather than him needed to be aggressive to protect you or scare other dogs away to protect himself. Of course, you then need to be sure to interpret other dog's body language and determine what their intentions are. If they are aggressive or dominant, you can be sure you block their approach to your dog. Once your dog realizes that you are the boss and will protect them, they will relax a little more and usually that will decrease instances of aggression as well.
You also need to reward him when he behaves appropriately and the way you want him to. I suggest paper thin hot dogs for training purposes or chic***** *****ver. Dogs love working for them.
It will be helpful if you can find someone with a dog to help you once you have your dog listening to commands consistently. What you will do is have your dog on the leash. You will have your helper off in the distance. Your helper will gradually move their dog a bit closer to you preferably walking past your position in the distance. As long as your dog ignores them, you can give your dog praise and a treat. The second you see her fixate on the other dog or show any other sign of aggression (hair standing up, etc.) give your dog a correction by giving a short tug to get his attention off the dog and back on you and a firm low toned "NO". It shouldn't take your dog long to realize you will not tolerate the aggression and that if she ignores the other dog, she gets treats. Once this happens you can repeat the training moving the other dog closer until she is no longer trying to lunge at other dogs. You will need to practice this when you and your dog are walking as well.
Let me give you a site that is helpful for teaching you how to teach your dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
Training works best if you train at least 30 minutes a day (two 15 minute sessions). I would start making your dog work via the Nothing in life is free program (NILF). It is outlined below.
An alternate methods for helping dogs that are acting aggression toward other dogs. It is the Bat method which you can read about here:
I personally don't like dog parks as often there are dogs that are aggressive toward other dogs and many times the owner does not have control over them. Often it only takes one attack from a dog to trigger fear aggression in a dog. This may have happened to Willie. A better way of interacting with other dogs is in a controlled Atmosphere such as a training class. This is also a good place to find a playmate for Willie. The best playmate would be a spayed female of similar size and age. Find a dog that he gets along with initially and then introduce them away from home initially. I suggest a tennis court that isn't being used. If they initially get along, keep the leashes attached and let them interact trailing the leashes. If there is not fighting after 15 minutes or so, you should be safe to remove the leashes and let them play. If they do have an altercation, you can use the trailing leashes to control them.
These techniques should help his aggression and give you better control of him.
I hope this information is helpful to you. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have . If you do find this helpful, please take this opportunity to rate my answer positively so I am compensated for my time.
If you have questions in the future that you wish me to answer, you may click here and bookmark the page or make it a favorite. It is best to put my name "JANE" in the question as well.
Since there have been recalls on certain foods, please check the following site to be sure the food your animals eat is not affected. If it is affected, contact your vet as soon as possible. Have your dog seen if they have any symptoms.