For our farm, we got a PetSmart system (NorthernTool.com) and put in 1500 feet of buried wire (not sure how many acres that is - about 4.5?) and it took about two days to train our black and tan coon hound. I walked her around the whole area on a long rope, so she could wander close if she chose, or stay away. The system lets you set it on beep only at first (while training her to the flags they provide) and then ratchet up the juice as needed. We did about five circuits around the perimeter. Since then she has run through it about three times and I have ratcheted the power up to the mid-point. She now stops short, regardless of deer, our other, less wander-prone, dog or the kids. As she learns the boundaries better it seems like it will work great.
Neigbors here in the city have their dog loose on a very busy road, constrained only by the electric fence. Not sure I would do that, but it has worked...so far.
Problem I had: I didn't need the tractor. The trench for the fence only had to be about 2-3 inches deep and I ran it along the edge of the field....too small a job for the tractor or at least for the implements I have (FEL). My pickax easily turned up the grass and in the woods portion, tractor would not have gone. Wire got buried by hand. And for that portion where there is old fence I ran the wire along the backside of the boards or barbed wire. System is supposed to work for up to 25 acres....I'd want to have some sort of a machine for that much...at our place you'de need to cut into the shale, cling to the side of some bluffs, muck through some wet bottoms....this in addition to the easy parts in the soft pine forest floor or open fields ... aw hell might as well do it by hand.
Ran it through an old pipe to go under the driveway and tried to stay into edge of woods so tractor weight won't cut wire driving in fields.
Good luck.The dog loves being freer.
Chas