i HATE invisible fencing for many reasons:
* a friend had invisible fencing, it didnt stop a large stray dog entering her yard and killing her young shepard.
* Ive seen dogs as small as chihuahuas run through the invisible fence during a high drive moemnt without a second glance. however these dogs that break through the invisifencing often do not want to return home because they know that comming back in will hurt and well now they dont have the moment of drive to ignore the pain.
* Ive known of dogs stolen because invisible fencing is just as easy to walk on over remove the dogs collar and walk off with the dog.
* and ive seen strong willed dogs run right into traffic, straight through an invisible fence after a squirren and get hit by a car.
my other problem is ive personally put the collar on myself on lowest setting and felt the shock, its not plesent but even on high seting any dog in the middle of a strong drive moment (ie a manic squirrel or cat chaser) wont even feel that intial shock as they cross the barrier, but they sure as hell wont want to cross the barrier to come home. ive seen many dogs with invisible fence collars wandering (round here its a big fad because "people dont like the look of fences") there all cases where theyve chased something or someone right out of the yard and are you gonna go home if you know as soon as you cross that line your gonna get zapped?
i feel much more secure putting a chainlink fance up, and if your realy worried about escapage, spend a little extra and dig a trench burry chicken wire about 3 ft down and splayed inward then burry it and attatch to a pricivy fence, on top of the privicy fence attatch more chicken wire spayed inward towards the yard to the top. its the set up i have for a couple of my rehab pens for cyotes who tend to climb and dig.
ive found a 6 ft fence of any kind will keep MOST dogs in (some dogs can climb chainlink) for those with climbers grow fast growing vines up the fencing to "block" foot holes.