To say there are no flies on any one means that the person thus eulogized is sound, is all right. Slang.
1888. There are no flies on St. Louis, or the St. Louis delegation either.Missouri Republican, Feb. 24 (Farmer).
1888. THERE AINT NO FLIES ON HIM, signifies that he is not quiet long enough for moss to grow on his heels, that he is wide awake.Detroit Free Press, Aug. 25. (Farmer and Henley, Slang and its Analogues, 1893).
*** This interpretation strikes the compiler as exceptional. But why did not the D. F. P. say not quiet long enough for flies to rest upon him?