You just have to keep trying. Two years ago I called at a new farm and the first 5 times I called there I called in gray foxes and either shot or missed them. Ever since then I haven't got a thing on that farm but I know there are foxes on it. I also know from scouting there that there are fox holes in a bank close to where I call. So either they are in their holes or out hunting to far away to hear my call. I personally don't believe that there is a fox that will hear my call and not come to check it out. Lots of times I have seen a fox, called to it, and it came charging in every time. Don't give up and one of these nights you are gonna have a gray come charging in. I have even had them come up to my fox pro and cock their heads into the speaker end while the sound (rodent distress) was blaring out. Needless to say, those fox didn't live to tell about it.