If they're not coming to the call to start with, a decoy won't change the out come.
Make sure you're getting into your blind, and getting your call placed, without them knowing that you're there. Some times they simply won't come to the call, any call. You've tried it once, now next time, try some different sounds. It's amazing how one sound won't bring a coyote, but another sound will.
If you do the same thing over and over and don't get'em called and killed, they will only get harder to call in.