Some of our sheep had great hooves when they came to us, which then weakened and cracked after a few months with us. We put
Zinc Rich Rockies licks in all of our fields, and I'm convinced that has made a big difference.
The key thing is to protect the blocks from the rain, or they just disappear. We made holders (
details here) for them, and they now last for ages.
Also, as Shep53 says, we footvaxed our flock a year ago. It's a nasty vaccine, and some folks say you should really cull affected animals instead, so I really toiled over the decision. However, we haven't seen ANY scald or footrot since we vaccinated, so in my mind it was definitely worthwhile.
HTH!