So it's either something you're doing wrong while progressing thru that set... such as not watching your own fidgeting/movements while on your sit, and they're seeing you. Or, time of day happens to not coincide with when they elect to be in that area. Just like us they learn how the critters they are after only seem to come out in this spot at this time of day, etc.Probably a moot point. At this rate I might as well not take a gun.
Haven't needed it yet.
Think I'm @ 3 dozen sets and have seen nothing with hair.
OR...
It's simply that you've found where they are NOT at. And need to methodically proceed from there.
A huge part of how things get to survive to the next day is simply the vastness of the habitats they live within. And how that provides for a high opportunity for that critter and it's predators to have a low occurrence of being in the same place at the same time.
As hunters we just try to apply our critical thinking skills to what we've observed of their behaviours to hopefully use that to our advantage when we can.
And even when it's an area where you've personally laid eyes on coyotes trotting thru... more than once!... you STILL may end up doing a ton of sets before one of those lil bastards FINALLY decides to try coming in to the calling.
That's usually when ya gotta experiment with trying new call sounds that'd be unlikely used before by others in that area. Things like sounds of domesticated puppies, or kittens, for example. Heck I'd even contemplated trying to record my little Chihuahua we had, thinking that'd really amp'em u to come swoop in.