I'm so sorry to hear Presley has giardia. I found out Angel had it after I took her for a puppy assessment at the vet's as part of the contract w/ the breeders. You can read the thread here:
http://www.yorkietalk.com/forums/showthread.php?t=44285.
I was told to shampoo her bum after every bowel movement as the cysts can cling to their hair. I bleached her pen area and floors w/ 1 oz. of bleach mixed w/ 30 oz. of water to disinfect things. I also washed her toys and bedding in the washing machine w/ hot water and dried them in the dryer w/ hot heat. To disinfect plastic toys, I was told to let them sit in the mixture of bleach and water and then pour hot water over them. Then I let them air dry or used tissue to dry them. I fed Angel pineapple every day to prevent her from eating her stool as they can reinfect themselves that way, though I've never seen her eat her poo.
Humans can get infected by animals and vice versa. Just wash your hands after handling your dog and his stool. Dogs can get it from stagnant/contaminated water, eating other dogs' poo that's infected w/ the parasite and I would think sniffing another dogs' bums as cysts could be in their hair. Keep your dog away from other dogs' poo and bird droppings. I live in Canada, and the breeder said it's common in Canadian geese.
After going through this experience, I'm paranoid about taking Angel outside. I've been trying to get her used to her harness and leash inside the house, but we haven't gone outside for a walk yet. I'm planning to walk her on the road on a dead end street and not grass at first.