To prevent obesity, add fruit to his diet instead of fatty meats. Feed him whole rodents and a lot of diced cantalope, peeled apples (mine don't like the peel), pears, mango, cheeries, grapes, whatever he likes. Like people, he'll stay trimmer on a leaner diet. He still needs protein, but let it come from a lean source like lean rodents, fish, and chicken, and not from fatty ground turkey or canned foods.