I use a hanging salt lick
My horse is lame so a pasture/paddock is not an option because he is only allowed to walk on flat ground and he is not allowed to trot, he has to be stabled for three to four weeks and its the end of week one and he is getting pushy and bored definitely not himself, thanks though.
Put your horse in the pasture if that's an option. Horses should be horses. At shows when my horses have to be stalled I make sure that my horses are beside each other and can see each other. The also get hay in a hay net so that they have to work harder for it. They also get excercised a few times a day when they have to be stalled
Use a type up lick coz they can play with it too rather than just one on the ground or on a wall. Just be prepared for a lot of banging sounds if tied to a wall
Put your favourite horse treat (carrot, apple, peppermints, watermelon) in a container of water and freeze it and it makes like a treat lick
They have little balls now that you can put treats in, and as the horse plays with it the treats fall out! Otherwise licks, mirrors etc keep them occupied
put water and apples or carrots into a cup with a rope. then freeze it and it makes a pony popsicle! it also keeps them cooled down :)
You can hang a slow feeding hay net or give the horse a ball or other horse friendly toys. Hope this helps :)