Fear Aggression

Hey,

Thanks for your post, hopefully I can help. Does he show the same aggression on-lead and off-lead?? One option is that it may be a Lead-associated aggression:

Dogs are compulsively social animals. When most dogs spot another dog or a person on the street, they are highly motivated to approach and investigate. If they are on lead at the time then they are restricted from doing this which leads to frustration. This frustration translates into increased excitement and agitation, which can be alarming to the owner, who may then deliberately hold the dog back, tense up before encounters or even punish the dog.
This starts an association between the sight of dogs and people and frustration as well as owner tension and possibly punishment. A vicious cycle is then born and may lead to aggression towards you, the owner, or the person/animal of interest. This and the fact that they are guarding you is why more aggressive behaviour arises on-lead than off.

Part of the solution is recognizing how unnatural it is for dogs to meet other dogs without the freedom to approach, sniff etc. You should allow him to approach and investigate friendly dogs but only let them do so after they have performed a "please may I" command such as "sit".

Due to the problem being a recent change I think this should be enough, however if it was a chronic case of lead-associated aggression, a combination of disocciation(making the lead experience a positive experience), obedience training and controlled socialisation may be needed.

Let me know what you think,

Becks