This was pretty amazing. We have an ‘invisible fence’ for the dogs. I installed it myself years ago. It’s just a single strand of wire that wraps around our entire yard that must transmit some kind of signal to the dog’s collar so when they get close to it, the collar starts beeping. If the dog decides they want to ignore the warning and they go closer to the wire, it sends out a jolt of electricity that would fry a cow. I know it will fry a cow because I tried it on my finger. It took a good 5 minutes to get any feeling back. Last fall the little box that sits inside the house and to which the wire is connected, started beeping. That means the wire was cut. Second time that happened… First time was at this spot where the wire had been sticking out of the ground for years. I was too lazy to fix it until it broke. Needless to say, that one was easy to find. So I ask you… how do you find where a broken wire that’s underground, running for hundreds of yards? I don’t know of any way to do it, so I called my brother in law who’s a brilliant electrician. Apparently, there’s some kind of device used to do this but he didn’t have one and didn’t know much about it. Back to square one. Not wanting to put a whole new wire in (an all day affair if I had the right tools which I don’t) I searched the internet for a solution and found this: http://www.instructables.com/id/How-to-find-a-break-in-an-invisible-dog-fence/?ALLSTEPS They tell you to buy an "RF Choke" from Radio Shack and install it as they show in the picture. It only cost $1.50 so I had nothing to lose. Then I duct taped a small battery operated AM radio to the end of a broom handle, tuned it to the right frequency, and walked around the yard sweeping this thing across the ground like one of those metal detectors. It worked great! I couldn't believe it was so easy. I’m telling you all this so you know how to fix an invisible fence in the future, so please take notes. The radio made a distinct, static noise as I waved it just inches off the ground, but only when it was directly above the wire. The radio went virtually silent if more than a few inches to either side of the wire. Once I got close to the break, the signal gradually disappeared. I thought it might only be because of all the tree branches and things in the area so I walked past the dead area, about 40 feet away, and came up from the opposite direction. Sure enough the signal stopped about 20 feet away from where I lost the signal coming from the opposite direction. I marked the two spots and started clearing away the brush and found a ground hog hole. The ends of the wire were sticking up out of it. Apparently the ground hog had dug his home, busted the wire and neglected to repair it. Thoughtless bugger. What amazed me though was how this tiny AM radio was able to pick up a signal from the wire. It was VERY accurate. If the radio wasn't within a few inches to either side, it went silent. I’m not sure why the signal fades 10 feet away from the break in the wire. I think it’s either magic, or it has something to do with the wavelength the wire transmits at. Not sure which but it’s probably something the CIA, NSA and some of the folks here know all about. As you can see, I’m easily amazed… So tell me something – why did the signal fade away about 10 feet from the break and how could you calculate that? And how does that RF choke work??? Any other insights to this device?