We have two beautiful granite slab steps on the path up to our house... however, they are smooth granite on the tops - which makes them dangerously slippy in the rain.

Any ideas for how I can make them less slippy?

I tried painting strips of diluted silicone calk on them - which worked fine, but the thin layer of caulk picked up dirt over time and has worn off now.

Can I etch them with some sort of acid to take away the smooth surface? Or maybe cut a few very shallow grooves in them with a circular saw and masonry blade?

They are too big to remove, so whatever I do it needs to be done in-place.