With all the leaves on the greound and all the grass drying out it is almost next to impossible to stalk in that close this time of year. Maybe you are also not taking enough time that last 100 yards can take a long time ( hours ) if need be. You can try taking off your boots and putting on an extra pair of wool socks that may help you out a little.
Better yet buy a blind. I went out yesterday set up in an open field with my Double bull in a spot deer usually enter the field at, 2 hours later I was surrounded in mule deer does and a small buck. Tag filled.