Q: When is an invisible fence not invisible?
A: When your father-in-law plows it up.
When that happens, it is not only visible, but audible. The controller beeps to let you know there's a break in the line. When you unplug it, it beeps to let you know that the unit isn't getting power. Very helpful.
I posted earlier that the Invisible Fence company had top-notch service, and I'll update that report after I hear about how they handle this. I should get the update from the wife shortly and will post about it later. (I'm in Sacramento right now, so this is all second-hand at the moment).
Oh... and before anyone says "Lucky fucker is in California" let me just say that the weather followed me here: rain turning to snow, high of 50 degrees.