Increasingly pet owners are complaining about dogs that seem to go crazy on leash when they see other dogs, people or wildlife but are fine off leash. So what's going on?
Dogs are inherently social creatures and like to investigate their world. When off leash they can determine how to approach (distance, speed, posture, if to approach at all, etc) but we add a leash to the situation and suddenly the dog has no choices at all. Add in the fact that very few humans that are aware of dog body language and social behaviour and there's disaster. Scared dogs learn that they are forced to interact with unknowns in their environment in an unpleasant way. Hyper/friendly dogs learn that they can't get access to exciting stimuli and become frustrated.
And then leash reactivity happens. That's the behaviour where a dog is at the end of his/her leash barking/lunging/growling, etc or running around in circles with the same results. Most of the time the owners are really embarrassed and don't know what to do.
This is definitely the time to call in a positive reinforcement trainer to help you come up with a plan. Fearful dogs will need different protocols than hyper/friendly dogs. A good dog trainer can spot the difference where most people can't. Sometimes a very scared dog looks hyper or aggressive. You won't get anywhere if you can't tell the difference.
Many training academies will offer special classes for dogs with these issues but I highly recommend you start with private one on one training. A lot of the work can start right in the home.
My own Miniature Schnauzer Heidi came to me as a fearful reactive dog. She would bark and have a fit at anything that moved (people, dogs, cats, birds, bikes, skateboards, leaves, etc). You wouldn't know it today. We worked slowly on desensitizing her to each environmental fear (and I mean slowly as it took well over a year) and at the same time participated in confidence building activities and fine tuned her obedience skills. Heidi now helps me work with other fearful reactive dogs as she can be a relaxing prescence. That's success! Help is out there and the longer you wait the worse it tends to get.