I just bought an electronic caller. I think the real key is calling where there happen to be coyotes at the moment. I don't know if you remember me shooting the hose biter several years ago? I called that coyote with a 45-50 year old mouth call and the squeaker from a dog toy, but I knew where we lived.
When tracking deer, some deer last overnight while others are chewed up by coyotes. I had a doe totally consumed in one night, and a year later I had a buck untouched in the same location. Coyotes move around, so calling locations need to span at least a half mile to a mile. A coyote's home range is 5-10 miles!
Good luck, I'm waiting for a success pic!