How can I make my solar landscape lighting "theft proof"?

We purchased 3 pairs of solar LED landscape lights. They are simply spiked into the ground with the exception of one light that will be attached to the house using screws.
I would love to find a way to semi-permanently anchor them into the ground so that no one steals them. I've attached a photo of the lights and what they look like once they are in the ground. -thank you!
q how can i make my solar landscape lighting theft proof
Please note: our lighting will spiked into dirt/mulch not grass.
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