I do not advise using salt blocks. Salt licks? Yes. Blocks? No. What you want to do is empty a bag of rock salt into a shallow hole in the ground, throw the dirt back in over the top and kind of chop it up a bit. This will keep the deer from getting at the salt directly. It will infuse itself a bit into the soil and the deer will get at the salt by pawing up the ground and eating the dirt. This is the cheapest solution. It is also the healthiest for the deer.
Blocks of pure salt or salt with additives give deer a chance to gorge on the salt. Supposedly this in turn causes them to gorge on water. They end up repeatedly filling their bellies with water instead of eating forage. By making the deer work at it, the deer eat less salt, drink less water and maintain better eating habits. At least that is what I read in D&DH a few years ago.
What I do know is that I can bury a bag 50# bag of rock salt in a 3'X6' pit dug out about 8 inches and there will be hoof prints in that spot for years. I know this, because I've had a few spots that I salted and then decided for various reasons to not replenish. As long as there is enough salt to keep the grass from growing over the top, there will be deer digging at it.
The other thing this sort of lick has going for it is that the deer get a lot of trace minerals out of the soil. FFKevin's recipe links are the same ones I recommend.
Remember, this is not like baiting. Deer stop being interested in salt as the summer progresses. I see very few visits after August. It habituates deer, especially does, to holding in a general area. Come fall, even though they are for the most part off the salt, they'll still be walking by. By November gun season, they've forgotten what salt is.
I think that salt got a bad rap, because up until the institution of modern seasons, folks would hunt over licks in the summer and decimate the deer. Teddy Roosevelt writes about this practice and abhorred it. By making modern seasons in the fall of the year, this weakness of the deer is no longer exploited. I've witnessed deer first hand in June and July. Yikes! Think of a Starbuck's line in the morning. I once had a lick 20 feet from the back fence of a neighborhood swim club. The deer would hit that salt all day and all night, even with screaming kids doing cannonballs off the board 20 yards away.
When it comes to dead-nuts certain ways to put deer under your stand in the fall, salt is not one of them. You want dead-nuts certain? Put your stand up next to an oak tree dropping acorns. THAT is dead-nuts certain.