I did some limited research before I had the last invisible fence put in. At that time, they didn't seem as dependable as the underground wire type. My 1st fence was about 6 acers. That was way too much. The dogs were always in trouble, digging up rabbit nests, chasing deer and other critters. 6 acers don't seem like much until your wandering around at night in your underwear looking for your dogs. Around an acer now.