Homemade floor protectors -- advice needed

Here's my situation: I have hardwood floors that I want to protect from my speakers' spikes. I could use those little support disks, but they're a pain when adjusting the speaker position (they move out of position, and then I poke holes in the floor). Instead, I was thinking of placing two stone "tablets" on the floor, and then putting the speakers on top of them. There's a shop nearby that will cut the stone to my specs, and then polish the sharp edges.

My question is, what kind of stone would work best? Granite, marble, or something else? And would some small rubber "feet" on the floor-side of the stone still allow the tablet to couple with the floor to reduce resonances further?

Any insights you can share would help!