They work well for average conditions and circumstances. However, they have their limitations when it comes to how aggressive the animal is and how bad he wants to get to something or how badly it is scared. Then that animal will do what it thinks it should do.
I had a fella tell me not to worry his dog was very well trained and respected the buried fence boundary. I was asked to notify all the immediate area homeowners as to what I was doing. I was setting up some traps in a neighboring field for a coyote complaint. The one house had a dog that was going nuts the whole time I was working in that pasture.
I finished the first set, and I added some lure and a little urine. I moved over to start making another set. I became aware that it got quiet but just thought that dog finally got tired of barking, or the owner may have taken him in to quiet it down. I don't know what prompted me to look up towards that house with the barking dog, but I am glad I did.
I thought what is that dark object running toward me. I mean he was hauling the mail. By the time I realized what I was seeing I jumped up and ran to my truck and jumped in. Another few seconds later I am not sure what would have happened? He jumped up and scratched at my door pretty good trying to get to me. I had to drive over to that house and blow my horn until that guy came out. That dog followed my truck back there. It was a Rottweiler.
I thought I may catch that dog but never did. So yes, they work until they don't.
