I love calling active den sites. Mainly because I figure I have a good chance of connecting. If the den entrance has frosty/frozen ring, it's a good bet.
If you were at the den and 'saw' what you were 'looking at', then you are able to determine the routes to and from den. By that, once a Fox, Coon or Coyote gets close to it's den, they usually take the same trail. These approach trails are important for my set up on den sites.
With the wind in your favor (cross wind or down wind) set up to kill Coyote on one of it's main den trails. It will feel comfortable on this trail and use it without thinking or second guessing, if you set up for this approach.
I use mouth call for Coyote. Near den sites, Coyote challenge barks, yips, brief howl, barks & yips work in my area. At times it's a game of chess, Coyote responds with a bark or barks, then I answer with the same sound or sounds. Then I usually give 'em the cold treatment, I wait. They just have to check out this intruder near their den, for the most part.
One and Done, draw backs to Den sites this time of year...
If you walk all over the site or kill or miss or muff chance at Coyote...the pair or remaining mate will usually leave this site. Coyote don't like pressure at their den and will pack up and move. But you know they are there...go get 'em for sure!!