What a charming thread! Here's a few I've come across...

"In dog training, jerk is a noun, not a verb."
-- Dr. Dennis Fetko

"When its raining cats and dogs, be careful not to step in poodles."
--Unknown

"If your dog thinks you're the greatest person in the world, don't seek a second opinion."
--Jim Fiebig

"Blessed is the person who has earned the love of an old dog."
--Sydney Jeanne Seward

"Thorns may hurt you, men desert you, sunlight turn to fog;
but you're never friendless ever, if you have a dog."
--Douglas Mallock

"Scratch a dog and you'll find a permanent job."
-- Franklin P. Jones