We have an invisible "wireless" fence. The base unit is about the size of a breadmaker - actually looks like one to a degree. It runs off 120V. We bought ours at Home Depot - I think for around $250. It is a fantastic product - and no need to run wires around the yard.
PetSafe Wireless Fence | Instant Dog Fence PIF 300
We have a corner lot - around 3/4 an acre and we have the base unit in the main front hallway beside a curio cabinet. The dogs (45lb sheppard mix and a 55lb lab) can each go all the way to the front sidewalk, side yard sidewalk, the back yard property line and just over to the neighbors driveway.
The only complaint we have is that the dog collars are battery operated, designed to require a specific battery replacement offered by the mfr at about $5 a pop. We replace ours every 3 months or so.
EDIT: Failed to mention, both dogs are inside dogs. Let outside to do their business/exercise running after squirrels and little kids that wander onto the yard (JK!)