Go with coyote vocalizations. Start with an interrogation howl, then a female invitation howl, then mix in some female whimpers. If you get one to answer back, immediately go to a male challenge howl-almost try to cut him off if you are fast enough with the call. A pup distress will work too. They are pairing up now and growing more intolerant of intruders in their territory especially with the alpha pair. It's tough right now, but I think that will give you the best chance of calling one in this time of year. In about 3 months it will go from the hardest time of year to the easiest for calling. Then just give them an ear full of pup distress all day long and bring plenty of bullets! Till then be prepared for some tough calling.