I'm sure there are many horror stories out there too though. Alot can happen. I think that it can work out for you, but I would suggest using caution and never leaving them alone together
I agree.

English mastiffs are traditionally a calm, even-tempered, good-natured dog. My friend brought two GIANT mastiffs to visit us once, and they basically lay in the middle of the floor and snored, and let my chihuahuas and fox terriers sniff them, climb on them and generally act like idiots.

However, a good part of ANY dog's behavior is how it is raised and trained.

A big dog, even the sweetest, most gentle and kind big dog, can accidently hurt a small dog ... especially when the big dog is a huge, awkward, silly adolescent.