you have to keep after it,right now is probably the most difficult time of the year to call a coyote.you must be very stealthy and scent free as bowfisher said,I also use fox pee or racoon pee as a cover around the caller on grass,leaves or misted in the air.next is dont howl to much a couple of long friendly howls will do followed by breeding yips then wait ten or fifteen minutes,the whole howling and yips shouldn't last much over 20-30seconds at first then on the second howling and yips about the same,I usually make a set for about an hour when howling,they dont come as fast usually,but they may rush in.if you know your howls and a coyote challenges you,give him a challenge howl back this usually excites them and they come.a female invitation howl is also succesful sometimes,since the females are more territorial towards females then males.just keep trying it may takes several sets to even see a coyote,here in KY if I could see a coyote one in every ten set ups all year,I would be happy.I can usually do this early in the fall,but now that every body that hunts,deer,rabbit,squirrel,quaill,doves or anything has shot at them if they saw one they are as wary as any animal out there.not to mention they may have been called in and missed or busted the hunter,this makes them smart and sometimes uncallable.just hang in and you will score,and next fall it gets a lot easier when a new bunch of 25lb yearlings are racing each other to get to your calls,GOOD LUCK AND KEEP HOWLING.