In many cases, regular bathing with a pet shampoo formulated to reduce smells will do the trick.
Tartar buildup can cause bad breath. Take your dog or cat to the vet regularly for dental cleaning.
Ear infections, anal gland infections and dermatitis can also produce bad smells; check with your vet.
The problem may be hormonal - the smell may have been designed by nature for sexual attraction. Neutering the animal is the only solution.
If carpeting or upholstery smells after a pet 'accident', sprinkle it with bicarbonate of soda or cornflour and leave it for several hours. Brush off the excess, then vacuum. If that fails, try one of the new bacteria-enzyme solutions available at your vet's surgery or pet shops. But note that they can only be used on water-safe fabrics.
The sight of other cats in your garden maybe causing your tom to spray. Close the curtains when you go out or spot an interloper.
If your cat tends to spray the furniture, protect the upholstery with a finishing spray so that it won't absorb the smell. If he favours one spot, attach a matching piece of fabric that you can detach and clean. However, recurrent spraying may be a sign of a medical problem; check with your vet, who may also be able to suggest effective ways of training your cat to stop spraying.
If possible, keep all pet paraphernalia - beds, toys, litter boxes - in rooms with hard floors and hard-surfaced furnishings. Upholstery and carpeting absorb odours.
A cat will pick up the scent of other animals when it stays at the vet or a cat home. This may cause your other cats to attack it when it returns home. Put some kind of natural fragrance (such as vanilla essence) on all of your pets for several days to prevent this.
