Coyotes have enough memory capacity to figure out that if it was dangerous yesterday and the day before, it is still dangerous. In other words, if you go into the same area and use the same sounds and set up in the same spot 2 - 3 times a week, then they've got your number and you will need to make some changes to how you approach the area, the sounds you use, the time of day, etc. If you're calling to the same coyotes over and over, then at this point, they will be very hard to fool! Make some changes!