The purpose of an underground fence is to teach your dog boundaries. First you teach them where there allowed to go, and then the fence is just "back up" in case they don't listen to your training. So how well does your dog listen? Would it respect the boundaries you put in place? If you have a smart dog that will listen to where its allowed to go, I don't think you'd need anything fancy, the cheapest one would probably do. If you have a dog that will not respect these boundaries it'll cause more harm then good with an underground fence, they'll run through it, and then be to scared to cross back over because they'll get a shock then too. It also depends on the breed of dog you have, I've heard of so many huskies that will not respect an underground fence and will run through it no matter what. If you have a hard headed dog i wouldn't use one. I'm not trying to sound negative or anything, but it's just my opinion on them

if your dog won't listen, I'd recommend a dog run, and then maybe a cheap under ground fence when your out with the dog so that you can be there to correct it when it gets too close. But with an underground fence training is the most important part. So it really depends on your dog and how you think it'll react to the boundaries.