Pretty much do what everyone else does like the banding and bathing and stuff like that.
On my horses the have white on their legs I put polo wraps on them at night because they always seem to get at least one little spot on their white by morning.
Especially my two year old! Man do I miss my bay breeding stock paint mare that had not one spec of white on her! It was so easy!
My horses are blanketed and have a slinky on in the winter and that helps them from getting a winter coat and then in the summer they have a fly sheet with the neck piece on during the day and at night they get a slinky and a sheet on so my show horses are covered with something all year round unless I am not showing that season then they don't have anything on.