Free WoW Trick: When the enemy picks up your flag you get a message about who picks it up. As a priest, you should be able to do /target <player na

When the enemy picks up your flag you get a message about who picks it up. As a priest, you should be able to do /target <player name> of the flag carrier from anywhere on the map. Sometimes you can't though, which means you are outside rendering range, so you may need to be on the half of the map that your base is on.

After you do the /target you can then cast mindvision on the flag carrier, which means you can tell where the enemy is taking your flag so you can intercept it...