Only one thing to add. Replace the bag of flour with colored aquarium gravel, (green, brown, blue.) Animals and insects will eat the flour, wind will disperse it or rain will wash it away, but gravel will hang in there and small amounts are not likely to be noticed of you aren’t looking for it.
Your point is well taken, I would say flour for short term and colored gravel for longer term. Rags or aluminum cans stuck in unlikely spots also make good “natural” markers. You have to study the trail just the one correct way to notice the markers are linked in a pattern.