Correct me if I'm wrong, but the Feds can't enter any county for such exercises - legally - without the Sheriff's permission, right?
They can on federal lands. Like BLM, National Forest or such.
There is also this bullschidt:
http://en.wikipedia.org/wiki/Border_search_exceptionBorder Patrol (Feds) can enter private property with 100 miles of the border. You can not deny them access.