[Coda]

Aloe vera is toxic to cats. It's not just a question of ruining your plants; your poor kitties could die from it if they eat any. It's not quite the "one bite of the leaf and you're looking at kidney failure" that some kinds of lilies are, but it's still not good.

I would recommend a greenhouse, or put the plants outside. Stuff to deter them won't be enough, especially if they've already established for themselves that this is a thing they can mess with.

EDIT: Aloe is toxic to humans, too, for the record. Safe on the skin and good for burns, yeah, and the white inner pulp (but NOT the green inner skin that's right up against the pulp) does have some reputed health benefits in reasonable amounts (there are ways to prepare it that remove the toxin but it also reduces the health benefit), but too much of it causes intestinal distress, diarrhea, stomach pain, cramps, kidney trouble, blood in the urine, heart disturbances, potassium deficiency, muscle weakness...