I recently moved with my mastiff. We live on 3 acres in the country. Our road isn't super busy but we get some cars and walkers. My mastiff now is going on the road and wanting to chase cars at times or protect his property. He doesn't listen when called when he does that. Has anyone had luck with a shock collar or undergoing fence for a mastiff?? My mastiff is super sensitive and I don't how he would response to a shock collar or even find one big enough for his neck. Putting up a fence is not an option as it would be too expensive....if I got an underground fence it woud just be for the part along the road the rest of the property is covered by trees and farm fields. Does anyone have any suggestions??