Can a Dog Get Parvo Again?

I was told by my vet that once a dog has parvo, it is pretty unlikely they will ever have a problem again. We found a stray German Shepherd puppy we named Bear that we took in at about 4 months old, and even though he had 3 out of 4 booster shots against parvo he came down with it. 5 days in doggy intensive care, and he was well enough to come home. The biggest concern was that the vet told us to make sure any other dogs that came into our yard are completely vaccinated against it because parvo stays in the ground for up to 2 years. We asked about cleaning and bleaching and he said it was not possible to be sure all of it was neutralized. It is simply not about removing vomit or poop, it is in their urine too and that is why it stays in the soil so long. Our big old Bear lived to love us for 17 years after that.