Sealers don't protect from etching. As far as buffing out the etching, you would have to have a professional marble/stone restorer come in to restore it.

Aqua Mix Stone Sealer is about the best on the market for adding some secondary stain protection and some tertiary durability. We trust no one else's products for sealing our customers tile, stone, and grout.

That said, there is not anything on the market taht I know of that will protect against etching, except care and maintenance. Sweeping anyhting that could get caught underfoot to etch them and door mats inside AND outside of doors to catch debris off the feet.

There are various stone restoration and stone honing tools, products, and service companies around that can come in and restore them, but its pretty costly unless you do it yourself.