re: Invisible(underground) dog fences-What features should I look for in a good one?

We would walk ours around the perimeter a few times early on, with the collar on, so she knew the limits. After that, we were able to remove a lot of the flags. Our dog never really tested it much. Every time we would take her past it, we would make her sit at the edge before we would tell her it was okay to cross. Works perfectly.