Covering food is just normal for some cats. Living out the world for instance, a momcat that has just had a litter will find a huge cache of food, she will eat what she can and bury the rest for later. Come back dig it up and bury what is left in another place. Perhaps you are feeding to much food? My vet is fond of saying "feed the cat, not the bowl."
Stinky gas can be caused by low-grade food, or impacted anal glands, or another health problem.
Scooting the rump on the carpet means either parasites or impacted glands. Sounds like your cat needs a vet visit.
Feed your cats the recommended amounts that are on the bag of food. If it's wet food, it states on the can how much to feed your furry friend!
Cats can develop yellow fat disease from having too much tuna. Tuna fish for humans doesn't contain amino acids. Cat's need an amino acid called taurine to maintain normal strength and function of the heart muscle. If you want to give your cat tuna, make sure it is made for cats. Cat tuna has amino acids added to it!