My Cousin has a boxer that could get out of any crate / kennel that you put him in. He has severe seperation anxiety so this was an issue, as they did not want him to be loose to hurt himself. After spending bunches of money on every containment device known to man they finally ordered a lion transporting crate from Africa. It looks like a little jail because its made of metal

but it does the trick! Hope you don't have to resort to that! Lol!