I am the queen of the underground fence! We have had ours since the doods were about 5months old. We have a farm in an area where dogs absolutely cannot roam free (sheep) and no way to fence properly. We love it! Doods get trained very quickly to listen for the tone and back away from the perimeter. After a while they just stay inside the safe area. We have about 2 acres in which they have free run, but they can't go outside. They do occassionally cross the line, usually because we have forgotten to put their receiver collars on or have forgotten to check the batteries. This is due to poor human training! WE have wildlife, who do get into the perimeter of course, but the doods won't chase them across the line. We spent a couple of weeks working with them to get them used to it at first. You gradually increase the temptations they learn to avoid. The static correction is NOT painful. It feels REALLY weird and like somethig you'd rather avoid. We found that our doods needed the collars that have an adjustable correction level and the longer prongs because the luscious doodle hair can interfere with the correction a little, but if you're willing to work with them a bit at first, and pay attention to things like changing batteries every so often, you'll be really happy with it. NOTE: It won't keep other dog OUT, so if part of your needs are to exclude other dogs, it won't work for you. (WE're way out in the country so other dogs coming by are pretty rare.)
WE learned how to install the fence without having to dig. If you are interested in this, send me a private message and I'll tell you how we did it......we "fenced" two acres in about 2 hours....!