I am reminded why I hate the Invisible Fence. Great invention, profitable company but for many dogs it can do more harm than good.
One example is a dog that is barking to get to a neighbor or anything across the street but can't because it's behind an "invisible fence". This can cause major frustration and escalate aggression. The dog can clearly see the stimulus (or stimuli) that makes it go into high arousal, when it can't get to the stimulus it becomes frustrated. If the dog gets too close to the edge and gets a "zap" then the frustration can escalate to aggression and also will most likely be associated in the dog's mind with the stimulus.
I was walking Riley, the handsome Golden Retriever I walk 2 days a week and there is a yard that is lined with big bushes along the street. Every few times I walk him I can hear this ruckus in the bushes and lo and behold I see a little Westie and a Lab mix dog that run furiously back and forth, often trying to make it through the bushes to get to us. They are frothing and frustrated that they can't get to us. They also think their antics are marvelous as we pass by calmly they are high-fiving saying to each other, "Ah, we did it again--chased off another person and their dog once again . . ."
Cross this one off of the Christmas list.