In the more pressured areas I hunt it seems the bucks have heard enough grunts and can calls that they dont respond to it anymore. I guess the first couple times they came into it and didnt find another deer they figured out something was up....or got shot. However on some more secluded land I hunt you can call deer in all day long,your buckslackof a response may have something to do with the area your hunting...just a thought. I also echo what the other guys said having something visual may seal the deal in getting him to respond.