We have had great results with a PetSafe RF 104. The wire is cheap 16 & 18 ga, surrounding about 5 acres. So long as we keep a fresh 9v in the collar, replacing every couple of months, it keeps our 80 lb. mutt in. He is reasonably bright, but a bit timid. I understand some tough dogs just power through it and take the shock. Ours doesn't. He did learn that as soon as the battery gets a little low, he can go down the twisted pair line from the house and get out where it splits to the perimeter loop. How he figured that, we'll never know.
The wire is strung along some fence above ground, scratched an inch or so in the ground at the edge of some grass, and embedded across a couple of blacktop roads with a masonry saw and cold patch. It has been broken perhaps 3 times, but we found the breaks and spliced it easily. The controller gives an alarm when the circuit is open.
All in all, we have been very pleased. It has shut down a growing neighborhood issue.