I know of a family that had a male and female English Mastiff. They were waiting until the female was a bit older to spay her so they seperated them in diffeent yards. The male was in the fornt yard, the female was in the back yard with no access on the sides of the house.
Weeeeeelllll, the male Mastiff chewed through the foundation of the house to get the female. Seriously. I saw the house after he was done. Those are some amazingly strong hormones working and I never would have beleived it if I hadn't seen it myself.
Personally, I don't want that kind of uber responsibility.....