I'm thinking about the wire being damaged, I'm remembering that my wife dug up the area where the line was to save some of her plants from the dogs. After installing the line, we decided that we needed another dog run, so I fenced in an area of the yard that went through her shade garden. Once the dogs where in there, the plants started to die, and she is borde line psychotic about her plants, so she dug them up to save them. We're pretty sure that she damaged the wire. That narrows down where I need to look for the damage, and where I'll start digging when things warm up again.
What I didn't know, and I still don't understand, is how a damaged wire can reduce the voltage in half? I thought that if it's broke, it's not working. If it's exposed to the soil, it's shorting out and tripping the breaker.