First, use 110 grn bullets, something designed for varmints. Try the Hornady V Max 110 grain.
Calling. Don't waste your time calling in one location for hours on end. You have been seen, smelled, or there are no coyotes around. Because this is a dairy farm, get an old fashioned cassette recorder and ask the owner to tape the cry of a newborn calf. This is what the coyotes are used to hearing out there. Dying rabbit calls have always worked for me, too. You could sneak the recorder into a brushy area and back off a bit. Also what works, a human baby crying! Sounds alot like a bawling calf.
Smell: no matter how you dope the wind or hunt into the wind or how much soap you use, there is always a scent unfamiliar to a wild animal on your clothes, gun, boots or whatever. I have some stuff that absolutely stinks but covers scent. I put a few drops of it downwind. I also bathe with non-deoderant soap and use clean clothes but after a few hours of hiking and sweating I am not sure it is much use.
Decoy: find a taxidermied rabbit or something like it and tie a feather to it's ear. When the feather starts moving in the wind a coyote can see it and zero in. It also keeps them from looking around. If you don't have the rabbit, tie a feather to a branch near the ground. I found a jackrabbit in a pawn shop. The decoy is placed away from your location.
Camo: They can see maybe better than they can smell. That is why a call placed at a remote location with a decoy works....sometimes. Even if it is only 25 yards away I think it works better.
If the farmer says he has coyotes they might be easy to find as they are probably used to seeing humans on the property. The rest is up to you. Dial in your rifle. 110 grain 308 MV 3150 fps +/-, zero @ 200, +1.5" @ 100, -7" @ 300. Also check the wind drift @ 10 and 20 mph. Tape this to your gunstock. Maybe you can borrow a rangefinder and laser the distances to landmarks around the property and make up a cheat sheet! Maybe find the property on Google Earth. It is kinda fun to do all the homework and then have it come together when you bust one at 300+ yards.
Another thing, when you call, do it into the wind. But sound travels and a coyote can zone in on the sound from any direction so look around. Or, position yourself so that a coyote's approach path is unlikely from the direction that your scent is flowing. Not sure if I phrased that correctly. If you are in hilly or rocky areas, a coyote is unlikely to climb down a cliff so that is where you sit as long as the wind is in your face. An animal will pick up movement first, even if you wear camo. Sit motionless as possible, round in the chamber, scope covers off, safety on, rifle in postion for smooth target acquitition, good stable shooting platform.
