I put hay in very tiny bunch under the fence line, or in small piles so my in-pen, horses have to walk around to eat. Also a friend, like a small goat, or mini will help your horse not be so lonely.
It is always best that your horse has constant access to hay, but if that is not possible make sure he gets some at least three times a day. You can get him toys to keep him entertained, like the roll-around ones mentioned in the article, and he may also like Likit brand treat toys. He should always have access to a salt block-my horses prefer the himalayan rock salt blocks.
One option is to invest in a slow feeder. I think they do their job very well, and I believe your horse will be happier and healthier too.
my horses ate all the grass from our fields, whatI did was build 3 slow feeders and it takes them most of the day to eat their hay..