Is there an alternative to rock salt to remove ice from flagstone?

Hi,

We just had a new flagstone walk installed at our home in Cincinnati. After it was installed we were told to never put rock salt on the walk, as it would damage it.

I have 2 questions. Our installer did not put a sealer on our walk. Should we seal it? If it is sealed, is it then OK to use rock salt?

Is there an alternative to rock salt? Where we live is often right on the border of winter storms... ie, we often get a lot of freezing rain. We just experienced a bout of freezing rain, covered by an inch or so of snow. This results in a very hazardous walk... tough to get the ice off... afraid to damage the walk by trying to chip it away. Any suggestions?

Appreciate any help you can provide! Lisa