[cypher]

Once the nails are overgrown then they need to be trimmed properly, if you take your ham to the vet to have it done they should be able to show you how to do it so you can do it yourself in future.
Stones don't really seem to do a lot, I have terracotta flower pots, saucers & granite tiles which can help to keep them worn down a little but Russian hams nails in particular do grow fast & usually need trimming at some point.