A person can learn a few things from an old dog. As the months slipped by and his infirmities mounted, Marley taught us mostly about life's uncompromising finiteness. Jenny and I were not quite middle-aged. Our children were young, our health good, and our retirement years still an unfathomable distance off on the horizon. It would have been easy to deny the inevitable creep of age, to pretend it might somehow pass us by. Marley would not afford us the luxury of such denial. As we watched him grow gray and deaf and creaky, there was no ignoring his mortality - or ours. Age sneaks up on us all, but it sneaks up on a dog with a swiftness that is both breathtaking and sobering.