Though whoever took sheep to a show with orf needs a stern talking to.
It will be on the hurdles etc that are in use at the show, especially if they still use wooden hurdles. Also a good place to pick up the likes of Johnes etc. if the show is on what normally is a grazed field...
However orf is not somehting to be massively concerned about, I have it sporadically coming to in both the sheep and the goats (sheep don't mix with the goats and never go to shows, goats go to shows all summer). If given good nutrition they will get over it fairly quickly, only time to watch is when it is on ewes' udders and then causes mastitis...
Don't think anything can prevent it...