Maybe a cardboard decoy of a cow or antelope? I've heard of people using those to get close to pronghorns. How high is the grass? Could you hide in it? The idea of digging a hole is a good one....how long can you last hiding in a hole? Or maybe you could cut across at a far end of the field into the ravine, sneak through it, and poke yourself just up over the edge at the right spot.