I have used various neoprene covers for my ACOGs in the past but found that they didn’t always fit well and they didn’t last all that long before they started splitting at the seams. The RCO ACOG Optic Cover from o241Tactical seems like a good solution for protection from dirt, dust, and scratches.
These simple covers are adjustable and fit loosely around the body of the optic so you don’t have to worry about the seams splitting. Like most of 0241Tactical’s line, they are available in an extremely wide variety of camo options.
Check out the 0241Tactical RCO ACOG Optic Cover.