I liked those holders for 4 pound blocks that you put on the wall. My horses liked them too - they are the perfect butt scratchers. So they ended up broken and now I have salted corroded screws in the wall sticking out that I can’t unscrew. Maybe if you put them in higher than I did mine that would work.
So now I put 4 pound blocks in small rubber feed tubs that are loose on the floor. Yes - they poop in them sometimes but you can take them outside and hose them. Yes frequently the salt gets thrown out of the tub but easily fixed. I did decide to put one of the tubs with the salt outside by the water trough. It gets overturned and I have to bring it in when it rains but that is easy to fix. And they use it more when it is next to their water and seems to encourage them to drink.