We got a rescue dog a few months ago and adore him. Vet thinks he is about 1 year, cavalier x maltese x shitzu - but who knows. He would've been on his own for a while, as he had really long hair when he got to the shelter. He's generally a good dog, until he's on the lead and sees another dog.
From the day we got him he would lung for anything - person, bike, dog... but only when he is on a lead. At the dog park, he loves playing with the other dogs and is very friendly/comfortable.
I've been able to stop him from lunging and barking at people and bikes by identifying it first, asking him to sit, and then rewarding (giving him a treat) for continuing to sit (treat after treat after treat until it is out of site or he focuses on something else). If I'm not able to identify it first and he begins to get excited/alert, I use his squeak toy, which typically works in getting his attention. This has also started to work in distracting him from barking dogs that are out of site.
However, god help us should he see another dog. Even after he's been to the dog park (so running and socialising), he's still lungs and bark, running from side to side if he sees another dog. Squeak toy - unnoticed. Asking him to sit - not a chance.
According to the vet, it is learned behaviour, and I know we need to get a grasp on it or it will get worse, but I have no idea how... He responds really well to the positive reinforcement training - picks up on things quite quickly. Any other ideas on how to control him? He gets into his 'state' and just goes crazy... Would be greatly appreciated!