Cur istud verbum te tam multum vexat? Iterum iterumque nos ista de re rogas. Rogandum autem est tibi usque intellegis istud. 
As before, don’t mix iste, ista, istud up with tuus, tua, tuum. They aren’t the same. Tuus, tua, tuum indicates possession independent of location. Iste, ista, istud indicates location independent of possession. Hic, haec, hoc is no more a synonym of meus, mea, meum than iste is of tuus.
Second, your understanding of Latin case as used in English is rather loose. If you are learning Latin, try formulating your example sentences in Latin (and cut out the middleman of English as it isn’t very structurally similar to Latin. Of course if what you want to learn is English, that’s another matter).
You wrote:
Gen: John, your dog is happy. In Latin that renders as (presuming iste=your, which it doesn’t):
Iohannis, iste canis est laetus.
You want something more like:
Gen: Your dog’s food smells.
Istius canis cibus putet.
(And for clarity: the dog is near you. He isn’t necessarily yours.)
Acc: John, there is your dog. In somewhat kludgy Latin to emphasize the near-to-you-ness of the dog:
Iohannis, istic est iste canis.
You want:
Acc: I see your dog.
Istum canem video.
Abl: John, where is your dog?
Iohannes, ubi est iste canis?
Of course, the answer to this question is likely Ablative case.
You want:
Abl: My food is in your dog.
Meus cibus est in isto cane.