Rock salt will dissolve faster than a block. I would put a salt block on top of the rock salt in a rotten stump if you can find it and after the rock salt dissolves the deer continually come to the block. I have noticed from the two salt blocks that I have that they lick and wattle a hole in the dirt around the block before licking the salt block. Its always a good ideal to have a trough of water near by as that will be there next stop. I usually watch them from my kitchen window regularly as I have seen some of the same deer for 3 or 4 yrs.
It usually takes a good year or two for the deer to startmaking it a part of there routine.

Bobby