Nothing works every time, at least I haven't found anything that does. I have used a hurt pup (ki yi) various barks, and a Dennis Kirk sound that's called, "Coyote killing a rabbit" also Canine Puppies, and Kitten Distress, and Rodent Squeals. Also, a couple minutes of silence, followed by extremely low volume rabbit distress.
The one that seems like it would be effective in exactly the situation you describe is the WT sound, coyotes fighting over food. If I had one I'd use it, but I'm not getting a WT, so I'd appreciate it if someone (Bob?) would dub the sound off their WT and send me a copy to evaluate. If there is a comercial source, I'd buy it, if I knew where to get it. I might also be interested in Magpie or Raven feeding sounds, if those are available somewhere. Digging or scratching sounds can draw a response where nothing else works. You can do this with a handy branch or scuffing your boot on some gravel, really kick up some gravel, etc. Make it quick though, and make no further movement.
If you have been detected, there are a few other remedies.
I might suggest moving. A coyote that has hung up in one direction, is a coyote that is more easily persuaded to respond from another direction, even if the distance is only 50 to 100 yards, if you can do it without being seen. Who knows, (?) but it is worth a try if they are stationary, and not inclined to leave or change location. You can get in your vehicle and drive a quarter mile, and accomplish the same thing. If there are two hunters, have one get up and leave, this works, if you have nothing better to do. The problem with attempting to lure in wised up coyotes is that you can call a couple stupid ones on your next stand with considerably less effort.
With that in mind, you have to decide where your time is better spent.
Good hunting. LB