Child Aggression

[lv4dogs]

I am thinking that someone, most likely a child is or has hurt or tormented Nicki when you are not home, through the fence. Some children may do it on purpose, others may not realize that they are actually causing harm to him.

It is very common for that happen & very common to see the same results you are experiencing.

I would never leave a dog unattended outside with those circumstances for that very reason, and a lot of others, someone may feed him food that doesn't agree with him or poison or someone can steel him.

Can you keep him indoors during the day?

If you catch this early you have a better chance at resolving the issue. Never leave him alone with any children and slowly start to socialize him again with kids. Making EVERY experience with kids a good one. Allow them to give him treats, nice gentle petting etc... and keep your eye out for any body languae or the like, if he starts to feel uncomfortable remove him from the situation immedietally and get him to an area that he feels comfortable with. never force him into any kind of socialization.
Obedience classes would help tremendously too.

How old is he?
Is he neutered?

[lv4dogs]

I see how old he is now.

Obedience classes would be very important at his age, he's going into his teenage stages where he may start to challenge you or others, this may be the case, but I am thinking more likely it is due from someone tormenting him or even a combination of both factors.