That's what you have young pups for! I know where the v.b. are and have had the grounds crew trim them since the system was built. The moles are our problem, filling up the pits, very seldom do they chew the wire, though a clean-out every season has always been specified in order to service the valves and check the color codes. In 90 zones, I've lost just one, and that was due to an incorrect as-built and lack of (my) supervision.