I am after some advice on how to cure or control my dogs aggressive behaviour to other dogs when he is on the lead. He is nearly 3yrs, crossbreed, nueted male, we got him as a rescue dog when he was 18mths. He used to be fine with all dogs, male/female on or off the lead, but over the past 4 mths or so he has started to, what can only be discribed as, go for the other dogs as he or they walk past him when he is on the lead. When he is off the lead he is still fine and full of fun and wants to play. I try hard not to act differently when he does attempt to lunge at another dog as I have heard that any kind of reaction from the owner can sometimes be seen as a reward for the said behaviour. Can anyone tell me why he has started to act in this way and what I can do to try to curb this behaviour. Thank you.

Dogs tend to "appear" more "aggressive" when on the lead because they feel trapped as they have no "escape route".  Try taking out a tasty treat that it gets at no other time and when a dog approaches ask the dog to look at you, sit etc something it already knows and treat for failure to react to dog; you should ensure that your dog is comfortable with dogs at a distance before increasing proximity and thereby the "threat".  Eventually you should have a dog that says "a dog oh goodee time for a treat" :D

You are right not to tighten the lead, shout, yell etc etc as the message the dog gets is "aha Obviously the arrival of this dog on the scene IS dangerous";  just ignore inappropriate behaviour.

You can spend hours, days, weeks wondering how it occurred but this will not address the problem :D

I just watched a big training show on this problem and they said that when on the leach and are aproched by another dog the way they are pulled back by the neck and standing in a foeward slanted position with thier chest out automatically forces them into an defensive position or agressive I cant remember the exact words,and the other dog picks up on it and may either come at your dog or just respond with body language and that may make your dog respond in a not so nice way,so they sugested using a gentil lead or harness.
Sorry about the spelling :))

hi i don't know if this would help, i've just bought my dog a harness that goes over the nose. this encourages the dog to stop pulling, simplifies training and corrects misbehaviours

a 'harness' that goes on the head(over the nose) is not called a harness but a head collar or Halti...
Archer.

i know what it is called i was trying to explain what it looks like and what effect it would have on the dog . the one i am using is a HALTI