The free range laws protect 'accidental' trespass by livestock, and the ranchers from being sued for damages they cause... and you can't harm the livestock that do stray- but they can't deliberately drive their cattle onto your property, either.

Call the local brand inspector, and get their take on it... they're usually really helpful, at least in my area.

While you can't harm or keep the cattle, you can "persuade" them to leave... cattle prods are acceptable in the industry, how about paintball/airsoft?

"Just tenderizing them for ya"