You can't stop it unless you separate or send in as suggested above. What breed are they? And do you definitely have all boars?
I doubt you will have boar taint. I have never actually met anyone who has had boar taint in finishing pigs. I have been given bacon from an old, working boar that was very strong. I also know someone who butched an old, working boar and it was fine.
People talk about it but no-one seems to have actually experienced it.