I would offer hime some gum or mints.
Just give him some gum that gets rid of bad breath.
Give them a toothbrush
what crawled in your mouth and died? or, you could just offer them a breath mint and hope they take the hint.
Offer them some breath mints and a bottle of scope.
i'd ask them what they had to eat, and hopefully they'd take a hint.
Just say umm I think you should try a new toothpaste I recommend colgate or maybe you could buy a tongue scrubber... Lol just say I had to tell you because I'm not the only one that notices.
You could try making a 'woof' noise every time he comes into the room. He'll figure it out soon enough.
Query what he'd been eating.
It may take several days of this question, but depending on his savi, he will eventually get the message without you being to forthright.
I would just offer them a breath buster bone and say I baked them special