Well, I've seen sausage dogs who were active and who remained healthy and hearty for about 98% of a lengthy lifespan, and I think that's good enough, Gurney. Most humans don't do that well.

Yes, their backs are vulnerable. However, we had one called "Valdy" and his back never failed him. He died finally at age 16, and his back was still fine, but his hind legs were getting pretty shaky.

I'm afraid, though, that you're quite right about the "lunp on a sofa" ones.