EOS secondary indices, how to extent?

EOS Programming
#1

indexed by “byowner”, how can also indexed by “PetType”?

TABLE pet {
    private:
        uint64_t id;
        name owner;
        name pet_name;
        uint64_t age;
        name type;

    public:

        pet(){}

        pet(
        uint64_t const _id, 
        name const & _owner,
        name const & _pet_name,
        uint64_t const  _age,
        name const & _type) :
            id(_id), 
            owner(_owner), 
            pet_name(_pet_name), 
            age(_age), 
            type(_type)
            {}

            uint64_t get_id() const { return id;}
            name get_owner() const {return owner;}
            uint64_t get_owner_value() const {return owner.value;}
            name get_pet_name() const {return pet_name;}
            uint64_t get_age() const {return age;}
            name get_type() const {return type;}

            
            uint64_t primary_key() const {return get_id();}

            EOSLIB_SERIALIZE(pet, (id)(owner)(pet_name)(age)(type) )
    };

   typedef eosio::multi_index<name("pets"), pet,
    eosio::indexed_by<name("byowner"), eosio::const_mem_fun<pet, uint64_t, &pet::get_owner_value>>
    > pets_table;