What can I feed my old dog ...?

It is the grain in the food that often causes gas. Gradually transition to a grain free food such as Taste of the Wild Pacific Stream. Use the food for treats. No table food. Adding yogurt, such as Activia, that is guaranteed to have live active bacteria may help. Exercise will move the gas out of the system.

You say nothing about actual age (other than "old), breed, size, if this is a "new" development or has been going on for some time, etc.

With so many things left unsaid, I would most certainly at least TALK it over with your vet, and yes, he/she will probably want to see the animal to check it over. However, you will be doing the right thing. Could just be old age and a diet adjustment might be in order. Could be an underlying medical issue .

meat bones and offal.

these are the three things only that a dog should eat, regardless of age.

Smells come from bacteria feeding on undigested food in the intestine. If you switch to a natural diet such as meat it may take a week for their systems to stabilize then most of the smells will be gone.

In the meantime you can feed them charcoal biscuits which will help reduce flatulence and smells. Good luck

Yea I would try feeding her all natural foods like the previous poster said. No foods with a lot of grease, so bacon, or any fully cooked meat. My dog has HORRIBLE smelling gas from bacon and other meats. I feed my dog all natural foods and dehydrate some sweet potatoes for treats as everything else gives him HORRIBLE gas! He can clear the house out in a jiffy though if I don't like the company ;)

Try an organic dog food

ex.) Artemis, Solid Gold, TOTW, Wellness CORE, Blue Buffalo Wilderness, Innova EVO, or you can go raw : )

Pancur or other parasite remedy might be more effective. Have the vet do a fecal and prescribe the best remedy.