What is the ruling on selling dog food, and what is the ruling on raising dogs for guarding homes?

There is no شرعًا (Islamically) any objection to working in the production of animal food, such as for cats and dogs, nor to selling these feeds. The sin of whoever raises them for purposes other than hunting or guarding falls upon them, not upon the seller, for feeding animals is Islamically مطلوب شرعًا (required).