[tsolomon]

What you need to do as pack leader is to let him know that this behavior is unacceptable. You can do this by setting up a situation where you can control the dog enough to send the message not to do it. I think that some type of remote training collar would be a last resort.

If you have your dog leashed in the yard, will he still charge another dog that is out front? The simplest of corrections done right at that time is where I would start. If he doesn't react when leashed, maybe you need to stand between the dog and fence and tell him to stop when he charges. Boxers are pretty smart and once you communicate that this isn't his job and his behavior is unacceptable to the pack leader, then you should be able to stop this. Plan on spending a day or two out in the yard working on this.

Can you get someone to walk a dog by a couple of times so you can work on modifying your dog's behavior? First with you in the yard and then from inside the house. He must be trained so that he understands that it is never ok to charge the fence regardless of where you are.

You must be ready to reward good behavior with a treat so that there is positive reinforcement for not charging. The clicker can help here as it provides that instant confirmation that his behavior is correct. You know your dog better than any trainer and all they can do is give you tools to try. Different dogs respond to different methods, which is why trainers often have multiple ways to accomplish a training goal.