I invested in a rat zapper at my last house (neighbor had a yard overgrown with ivy and blackberry so there was nothing I could do to eliminate the problem). It wasn't cheap, but it was EFFECTIVE!
http://www.amazon.com/Rat-Zapper-RZC001-Classic/dp/B002665ZTC
http://www.amazon.com/Rat-Zapper-RZC001-Classic/dp/B002665ZTC