Two dog owners

Two dog owners were bragging about the intelligence of their
pets.

"The brightest dog I ever had," said one, "was a Great Dane that
used to play cards. He was a whiz at poker, but finally a friend
complained about him and I had him put to sleep."

"You had him put to sleep, a bright dog like that? A dog like
that would be worth a million dollars."

"Had to", he replied, "Caught him using marked cards.