The guy who wrote the bill that Horn apparently thought gave him the right to go shoot unarmed people on his neighbor's property says it doesn't apply to a neighbor's property:
http://www.cbsnews.com/stories/2007/...=mostpop_story
"Under Texas law, people may use deadly force to protect their own property or to stop arson, burglary, robbery, theft or criminal mischief at night.
But the legislator who authored the "castle doctrine" bill told the Chronicle it was never intended to apply to a neighbor's property, to prompt a "'Law West of the Pecos' mentality or action," said Republican Sen. Jeff Wentworth. "You're supposed to be able to defend your own home, your own family, in your house, your place of business or your motor vehicle."