Burying is the key in my mind. Blocks and such give them too much. If they have to work at it, it does not make them as thirsty and therefore does not have them filling up with water right after. Just because the craving is there, does not mean it is a good idea to fill it. That craving is gone by hunting season anyway.
The only reason I use salt is to habituate the does into coming to the general area of my stands. All these ideas about promoting antler growth are highly over-hyped in my view. The ground around me is clay, but you dig down 6 inches and you start hitting limestone. There is all the calcium any deer is going to need.
Mixing Salt, rock salt, water softener pellets-- these all do about the same. Whatever you can get the cheapest is fine. I used to go out in March and replenish, but I am getting lazy. I'll probably do the deed over Memorial Day, just because the ground was so soggy. After a few years of dumping one bag a year in the same spot, you end up with enough residue that even skipping a year will not keep them from coming.
Effective? I did my original experiments with buried rock salt back in the 90's. I had a lick behind the neighborhood swim club, about 20 feet from the fence. I could bury a pound or two and come back 2 hours later and the deer would have been hitting on it, even though there were screaming kids just a few yards away.
