Hi Kathie,
An 8ft wall is pretty high so you would want to bury the wire either at the base of the wall or attach it approx 2-3 ft up on the wall off the ground. The dial on the transmitter adjusts the boundary width and the max you can turn it up to is about 10 ft. So having it on the very top will make it difficult to set a boundary. If you bury the wire at the base or attach it a few feet up you can adjust the boundary to around 4-6 feet and that will keep the cat that far away from the wall. Yes, you have to keep a continual loop around the yard.