Hang a couple of long "clothes lines" across the space and then hang all those free AOL CD's on the "long clothes lines".....birds do not like those "reflective" flashes....spooks em pretty good.
That in addition to your doggies will do well....
Also you can go to your local sporting goods store a gander or cabela's etc and get a few bottles of predator scent, add that to a few gallons of water in a pump up bug sprayer and add some cayenne pepper powder etc to make their food taste a bit crappy.....
Ya might also consider playing one of the johhny stewart coyote call tapes or CD's quietly over a speaker at night.....
Lots of passive possibilities......even a simple air-horn, the kind on top of a can of air will do the trick if it's the same flock...they'll learn.
Just some opinions.....
Great idea, coyote urine!! It's sold in sporting goods and pet food stores.