we have had a petsafe wireless for six or seven years now and love it. I run three units one on one end of the house, the other on the opposite end in the garage and one in the middle/front of the house. They can run up to 60' out from the house in all directions. If I go to the cabin I take one with and run it there and it keeps them at the cabin. If you wish to have a certain "shape" of a zone you can buy gps units that you basically map your zone with. Spendy though.
I have the Garmin Alpha which is GPS based. However, it does NOT shock the dog when he leaves the defined perimeter. All it does is give you an audible warning on the handheld to let you know the pup is out of the area. It is then up to you to fry the dog.
It works pretty well, but once in a while the collar gets confused and is off by anywhere from 50 ft to 100 yds (based on the handheld remote which is also a GPS). In those cases the owner thinks the dog is long gone when in reality the poor bastard is sitting right outside the door.
If you have lots of trees and other obstacles, I'd go with the in-ground version. The GPS systems (like mine) and the defined radio wave distance collars are all known to be a little unreliable in heavy cover/terrain. All depends on how close you can monitor him. My dog has now been on the GPS system for a year and until the neighbor lab-mutt shows up, he stays off the highway. It's getting to the point he's afraid of her. Mostly because she's the reason for about 98% of the times he's been zapped over the past year.
