Perhaps this is the one you are looking for:
A Dog's Plea(from Ann Landers, originally published in 1986)
Treat me kindly, my beloved friend, for no heart in all the world is more grateful for kindness than the loving heart of me.
Do not break my spirit with a stick, for though I might lick your hand between blows, your patience and understanding will more quickly teach me the things you would have me learn.
Speak to me often, for your voice is the world's sweetest music, as you must know by the fierce wagging of my tail when the sound of your footstep falls upon my waiting ear.
Please take me inside when it is cold and wet, for I am a domesticated animal, no longer accustomed to bitter elements. I ask no greater glory than the privilege of sitting at your feet beside the hearth.
Keep my pan filled with fresh water, for I cannot tell you when I suffer thirst.
Feed me clean food that I may stay well, to romp and play and do your bidding, to walk by your side and stand ready, willing and able to protect you with my life, should your life be in danger.
And, my friend, when I am very old and I no longer enjoy good health, hearing and sight, do no make heroic efforts to keep me going. I am not having any fun. Please see to it that my life is taken gently. I shall leave this earth knowing with the last breath I draw that my fate was always safest in your hands.