How do you keep a US Flag corners from fraying?

Darrell Vance
by Darrell Vance

Hi! I am a Patriot Guard Rider Ride Cpt. We use US Flags a lot during our funeral & military send offs to include welcoming them home. Our flags are starting to fray on the corners. What can I do to enforce the corners and repair? Can I use fishing line since it would be strong and wont be seen?