David, I get that question a lot!
I have hunted the same area for 11 seasons. I have access to 14 sections of private land, of which not all is huntable each year (crop rotation, moisture, etc.).
Some of the fields are wheat stubble, which was harvested using head-strippers, not cutting combines. This leaves the stubble about 24"-28" tall. So, there is plenty of cover for the birds to hunker-down in.
Also have some milo, which some of the farmers are also using combines set higher, leaving much of the leaf cover on the stalk. Also, very good cover, as this also hides them from hawks.
The CRP grasses are shorter, much of it being less than 18" tall.
The biggest factor I have found, over the years, is being quiet from the time we open the car doors. No talking in the field (other than "HEN"), and walking as quietly as possible. I never hunt with more than 4 hunters, and we always walk no further apart than 30'. One of the easiest ways for birds to stay alive is to stay put when we walk past. If we are close enough together, they can't stand it, and bust out when we are within 15' of them.
Secondarily is visibility. No-orange has proven itself, also. Those with orange don't have birds flush nearly as close as to those of us not wearing orange (my vest does have orange in the back, but only because I didn't find one with no orange at all). With the lighter cover, orange is visible from a long way away. Good for hunting the the woods, or tall cover, but not in row crops and sparse grass.
Yes, we see runners, but I also see runners when hunting with dogs. And, if you hunt row crops, the dogs crossing between rows make noise, and are also visible down the row to the birds.
I have learned over the years how to hunt my fields. It is a different technique than other areas, but hunters who pay attention to what I tell them, have success. Those that try to hunt how they hunt different cover in other areas, generally don't have success. If I got to go to South Dakota, I would rely entirely on those with experience in the heavy brush, etc.
While I would love to have a dog, our lifestyle does not lend itself to me having a great hunting partner. So, I adapt to what I have to work with. Limits on 80% of my hunting days seems to indicate I am doing something right.