Box walking simply indicates that the horse desires to walk. Increase turnout or if possible put the horse on a walker a couple of times a day.
If they still continue to do so, call a vet out as there could be an underlying cause
Depends on why the need to remedy. My boxwalking girl did herself an extreme injury which required her to remain as still as possible for weeks. As the alternative was no repair of injury and pts we crosstied her in front of a chain across the door and she settled very well.
When she went to Nationals at Hartpury she was in one of their bowfronted boxes in a big barn. She didn't boxwalk as there was so much going on.
She doesn't boxwalk if you make a 12 x 12 pen outside her box with hurdles and leave the door open - she's happy to stand in the outside space, which for most boxrest purposes is fine.
She doesn't boxwalk in a huge stable (18 x 12).
She doesn't boxwalk in an internal stable if her friends are in as well.
She boxwalks less if you put her hay on one side of the door and her water on the other. If you put one in the back corner she will do a circuit to get to it.
She is calmer with a chain across the doorway than having the door shut.
Things she hated as boxwalking remedies were; stable mirrors; things, even food, hanging from the ceiling; tv in front of her door; sheep as a companion.
And of course she doesn't boxwalk when she's turned out
cure for box walking??? TURNOUT as much as possible
If it's for box resting purposes then jemima has given you some good ideas but if it is not due to box rest the horse needs to be out, box walking can put a real strain on their legs as well as their mental wellbeing