Hi Becky, I'm glad that you found BPO, welcome! I'm mom to Daisy our Golden/Lab, Cassie a Pyr/? mix, and Sammy a Pyr and we've had two sweet Pyr girls that at the bridge now. We've had Pyrs since 1989 and I'm sure that we'll have a Pyr in our family for as long as we're able to care for them. Our first Pyr could go over a 6' dog-ear fence, and it took some really extraordinary precautions to keep her in, but that's not the norm. Our second, third & fourth Pyrs have all been fine with normal privacy fencing, but I wouldn't trust any Pyr ever with underground fencing for all of the reasons that everyone's explained. On top of the fact that they're bred to guard large territories, they also have extremely high pain tolerances and I seriously doubt that a shock would stop them from crossing the fence if they were determined to guard (which is what they do). However, they are really smart, so they will remember that it's there (once they're outside it) and they probably won't go back in, so it's doubly dangerous for this breed, like everyone's said. You can be sure that they'll cross it to guard or to roam, it's just in the genes. BTW, I have serious questions about any breeder that says that underground fencing will work with this breed.
This may just be the tip of the iceberg (as it were) with this breeder. I have never spoken with any good Pyr breeder that doesn't require strong, visible fencing with this breed, so personally I would be afraid of what else might be wrong.
Do they show the dogs, are the parents checked & clear of all major genetic defects, do they guarantee the pups, do they sell pups with a spay/neuter contract, will they rescue dogs from their breeding if they ever end up in Great Pyrenees Rescue? The best way that I've ever found to determine all of this is to contact the Pyr Rescue Coordinator in the breeder's area. They will know if this is a good breeder or not. Here's a link to GPCA's Rescue contacts, you'll find names & phone numbers here. I have a hunch that they'll be able to give you some good insight.
http://clubs.akc.org/gpca/gpcaresq.htmlPlease let us know what you decide. The most important thing is that you find the dog that will be right for your family, so that it has a happy, permanent home. I'm sure that you'll figure it all out with a bit of research. Again, welcome!
Modified to add: I'm sorry, I read your original post early this morning and I forgot some important points by the time I responded this evening! My mind is going to mush, I think.
I am so sorry for your loss. We lost our second pyr last year to cancer at 3 y/o and we miss her so much.
We just never have long enough with them, again I'm so sorry. I also just noticed that you are considering a rescue dog. I think that is wonderful! Though our first 2 pyrs came to us from breeders, Sammy came to us from rescue and Cass was rehomed to us by an elderly couple that couldn't care for her any longer. I think that rescue is a great way to find your new family member and save a life! I think that this sounds wonderful if you can work out the fencing questions. Agh, sorry this is soooo long!