Here is a demonstration of what happens to my Delta 4000 when it encounters a property surrounded by a working invisible dog fence. I couldn't believe how crazy my new metal detector was going as soon as I turned it on. I thought that maybe there was some interference caused by nearby underground electric cables, but nothing would correct the problem. I changed from All Metal1 to All Metal 2 to Discriminate. Still the same. I then turned the sensitivity to the lowest setting. That helped ever so slightly, but I still couldn't hunt without getting all kinds of false signals. I was about to quit when I remembered that the owners had two dogs. Sure enough, she had an invisible electric fence! Watch the video I made here http://www.youtube.com/watch?v=0meG7v3hkvI
MickTwin
MickTwin