Aaaaaagh! So frustrated housetraining dog

[Clark Fork Fantast]

Any possibility the difficulties could be breed specific? First Dog was a Shepherd-Lab mix and Present Dog is pure White Shepherd. We got First Dog when she was 8-9 weeks old, and with the help of bells and a good dog training book she was housebroken within two weeks...Present Dog is a rescue (1 year when we got her) who apparently was never allowed inside a house before, so the rescue people weren't sure if she was housebroken, but she must have been, or was an incredibly fast learner, because she only had one "accident" in the house within the first few days, and then learned to use the doggie door. So we've congratulated ourselves that we're really good at training dogs but we've probably just been extremely lucky with dogs who trained themselves! Any experience with some dog breeds being much more willing to be housebroken than others? We're beginning to think Present Dog may need a rescue sibling...