I would add to my earlier post that once we moved from the 13 acre property to a house on the edge of town with an acre and a half we had an invisible fence installed there too, just took the collars with us. When we moved in we had deer in the back yard of about an acre. Within weeks of the dogs being outside we never saw another deer, just the occasional whistle pig or skunk.
Once they learned where the wire was they never went near it. When we got our Standard Poodle she would test it every so often to make sure it was working. Smart dog!