Both ours have a salt lick. Jack disposes of his (large) one very quickly. Raf's (small one) lasts months, maybe a year. I only know he's been licking it by the damp patch I occasionally see underneath it.
If we've been doing something strenuous that's made him sweat I offer him an extra bucket of water with electrolytes in, as well as his fresh water, so he has the choice. Guaranteed that if we've been out somewhere like on a PR he'll drain the electrolyte water (and I give him another if he does) before he goes for the fresh water, whereas normally he won't touch the electrolyte one. I prefer to put it in his water because he's easily put off his feed if anything unusual goes in it and after a hard day he's often slow to eat his tea anyway.
On a daily basis he has Saracens Stamm 30 balancer because this seemed to have the highest concentrate of vits/mins when I was doing my research (admittedly several years ago). It's a pellet which he has in his feed, but he'll happily eat it on its own. He also has extra vitamin E but that's specific to his individual needs.
Poor Jack (retired) doesn't get anything other than a token feed with his Danilon (plus garlic and brewers yeast in the vain hope they do something to put off the flies) but he looks so well on it it's hard to believe he's lacking in anything.