In the misguided belief that Aloe pluridens provides therapeutic gel - that's my guess.

I'd leave them a note and a pile of Aloe vera leaves, advising them in the note to leave the pluridens alone (that's too bad about the plant - it sure can be a pretty one when folks leave it alone) and to take the leaves you cut for them. Maybe that's coddling the criminal but my other solution involves some cannon fire across the bow.

need to catch them in the act first.

That is such a shame! :( My guess would be the same...thinking they would get some therapeutic gel from it.

Since it is a repeat happening, leaving a LARGE note (maybe in plastic-if rain is expected) attached to the plant for a month or so, in hopes to educate them.

Warning:
An eye for an eye, an arm for an arm.
Do you want to keep both of yours?

Friends of mine once had a Koi pond they spent a fortune on. Racoons found the pond and figured it was meant to be an open air sushi bar. They found a brand of motion activated sprinkler that seemed to scare off the racoons eating their fish. Assuming the person stealing the leaves off your plants isn't vindictive (although anyone who would hack a gardener's plants down to the ground seems like they'd be that type), maybe a cold shower would calm their ardor for your plants?

got an arthritic Mexican grandma living next door to ya huh? We get a lot of calls from Mexican grandmas relatives cause it's a traditional Mexican folk remedy and grandma ate the leaves. Which made her sick. I'd look for the old lady/man with a cane.

Paraclesus I like the way you think!

MJ I need one of those sensors, that would work for neighbors, dogs, especially since I'm in the middle of digging a new pond.
Tally HO!

Bummer. good solutions here. I would move it. How about a motion detector to a camera with a flash. All that water might rot your succulents.

When I lived in Hawaii, the sense of community property that my neighbor exhibited was astounding. what is mine is mine and what is yours is mine. I caught my neighbor talking my aloe all the time. It turned out that his mom had bleeding ulcers so I brought him a lot of clippingss from my sisters place and a friends work place, and planted it in his back yard and told him to leave my non medical variety alone. Mine was good for making soap and was actually fairly caustic. He did leave it be after that but he didn't change his ways about other stuff. He would take my garden tools and I would take them back. He also took my dog and ate him and invited me over for the party.

Whoa! I lived in Hawaii and never had that kind of experience! Did you have a black dog?
Tally HO!