About a year ago, we decided there'd be no more stairs. I carried her from floor to floor, in and out of cars, and onto sofas and chairs like a stiff-legged suitcase. I would've done it forever.

Looking now at old photos, I'd forgotten all the changes. I never expected to have such an old dog. I never expected her to be old for so much of her life. She got used to the diminishment of her senses. She was a friend to my son, long into the years he'll remember.

Heidi was an athlete. She'd play fetch along the side of a mountain for hours. That was my attempt to exhaust her enough that her separation anxiety and boiling-hot prey drive wouldn't be so bad. It didn't work, but it was fun.

Heidi was an explorer. I didn't worry about letting her off leash. She ran ahead, but always looked back.

I took her everywhere. I don't remember all the places she's been. In my recent photo trawl, picking a random spot on the calendar, I found her standing in front of the Hollywood sign and shouted "what the fuck?".

Heidi was an odd and irreplaceable creature. The goat-like bleats and gravelly sighs can not be reproduced by even her greatest admirers. The best we've ever done is exaggerate them cartoonishly. This gets us closest to the truth.

Heidi was part of a package deal. If you shared your life with me in any capacity, Heidi was your loving friend and great annoyance. There was no me without Heidi. Even now, it's hard to believe there will have to be.

I took her home in 2010. She almost made it to 18. For all intents and purposes - and because there are still things about her I'll never know - let's say she did. She was the dog of a lifetime. I can no longer feel the weight of her. But I know I'll still find her, again and again, even as she wanders beyond my view.