Please do NOT hide things from rescues or shelters. Rescues have their reasons and they're just trying to make sure the best possible result is achieved. Pembrokes are very vulnerable to attacks by other dogs and invisible fences don't protect them from things (bigger dogs, coyote, raccoon) trying to get in. Some of the smaller Pems are under 20 lb and they look like a bratwurst sitting there in the yard; the rescues know that the collar will keep the Pem in but they don't want people to trust it to be a real fence. I screen owners all the time and I personally would rather have NO fence (so I know that the people are out with the dog and he or she is on a leash) than an invisible fence.
One solution is to put up a small, tightly fenced area where the dogs can go unsupervised, and rely on the invisible fence when you're outside with them. That way you can say truthfully that the dogs are behind a good fence but you can enjoy the freedom of a larger area when you want to play with the dogs.
