There are two other fairly common tapeworms, Taenia pisiformis, which infects dogs and Taenia taenaeformis, which infects cats. Taenia species of tapeworms have a life cycle that involves an intermediate host but it tends to be a small rodent (T. taenaeformis) or lagomorph (rabbit, T. pisiformis). As far as I know, it is necessary to eat the intermediate host to get these tapeworms, as well. Taenia taenaeformis seems to have the name Hydatigera taeniaforms now. There are some Taenia species that can be acquired by eating undercooked meat of goats, sheep and cattle but I don't know how commonly these infect dogs.  Their is also the most common tape worm that is caused by fleas but it is from the dog digesting fleas. So if they have eaten any type of dead animal or biting at another animal that may have fleas.  Your vet will have the best tape worm medicine but it has to be exclusive to tape worms.  Happy jack makes an over the counter one that is fairly good but still not as good as your vets...