If you have a dog...has your dog ever had lingering bad breath...halitosis?

what shall I do to make it smell pleasant....could my dog be sick?

There's lots of info and products on this subject.
Suggest you do a google search on "dog bad breath"
and you might start with this article:

http://www.ehow.com/how_2446_prevent-breath-pets.html

my dog's breath was terrible. It turned out he had some bad teeth that needed to be pulled. Now he's fine again. If you have one of those dogs that face is covered totally by hair, you could also just be sniffing the wrong end of the dog!

gum disease which can lead to other health problems.  Would be best to make an appt with your vet to find out for sure.  By the time I realized it was serious with my cat, she had to have several tooth extractions.  Hopefully, it's not too serious for your dog.

there could be a myraid of reasons why your dog has bad breath.  He could have a problem as simple as Coprophagia.

THAT WOULD EXPLAIN THE BAD BREATH.

EOM

Both my dogs had this problem. I took them to the vet and had their teeth cleaned. That fixed the problem. Greenie dog chews or bones will help prevent plaque and tartar build up.

First, you need to have your dog's teeth cleaned periodically.  This is somewhat expensive but is well worth the money.  This will take care of the odor problems most of the time.  If not, see a vet.

Your dog can get very sick from dirty teeth. I just had my dog's teeth cleaned and her breath is MUCH better as well as she is healthier. It's expensive but PetSmart has a "dog insurance" type of program that includes it. Check it out and take care of your little friend!