>How many hives in a row will cause a drifting problem?
more than one, not a wise guy answer but under the right (or wrong) conditions drifting can occur, the closer the hives are together the more often it occurs.
>I have heard about putting a marker. Like a piece of cloth on each hive hanging from the lid - each a different solid color - the bees will note the "address" of their home. Is this true? Anybody tried?
Bees recognize unique or different shapes and colors with the exception of red.
>What else can you do to decrease the chance of drifting?
Arrange your colonies in a semi-circle or spread out more loosely, not congested. make some colored squares, circles, traingles, colored lines, zig zags or whatever to set the individual hives uniqueness. Or paint each hive a different color.
Hope this helps--just my opinion.
"Younz" have a great day, I will.