What is the main conflict in Marley and Me by John Grogan?

John Grogan holds fond memories of his childhood pet, a mutt dog named Shaun. John and his newlywed wife, Jenny, are contemplating having children and decide that a dog will be good parenting practice. The couple visits a local breeder specializing in Labrador retrievers where Jenny picks out a rambunctious, gangly puppy. The puppy is named Marley after Bob Marley, whose music welcomed John and Jenny to South Florida. Marley proves to be nothing like Shaun. He is a salivating, headstrong, damage-effecting, barreling-through-life flash of yellow fur. Marley is kicked out of obedience school and almost barred from the Grogan household, but in the end turns out to be an excellent teacher of love and loyalty. Marley is the world's best worst dog.