We graduated to using flat wooden strips with 1" markings on them which seem to do the job but the best ones are (I'm now convinced) the ones we use for Napoleonics - namely hard wood square lengths. These you can get from B&Q for about 75p a metre. Slap on the preferred colour (or alternate colours in the preferred measurement) and there you are!
These we use for the Polemos Napoleonic rules - where movement is denoted by base width. I use red for troop movement and blue for artillery ranges. The red ones are in 1, 2, 2.5, 3, and 4 MU sizes and the blue reflect the calibre of the gun involved (from teeny 4 pounders to the mighty 12 pounder).
Red measuring sticks - 1 MU for line, 2MU for column. Simples!
Artillery measuring sticks - blue. Those Prussians are out of range of the 9lb gun
What's good about them is that they are easy to find and once placed don't move around, are very clear to see and give less room for creative measurement using the tape measure (you know what I mean). As seen above, the stick is placed in front of the unit which is then moved the length of the stick. Much less margin for error.
The same idea can be used for ancients - with (as in FOG) either a variety of sticks to denote 1", 2" etc. or one stick with multiple units (up to 14"). We find the former method better - especially when the armies get within shouting distance of each other. Again, a different colour could be used to denote ranges for archers, bolt shooters etc. - especially when you get into later medieval where any number of missile options (trebuchet anyone?) are available.
The line is safe - but the column is definitely in the danger zone!
They cost virtually nothing and can make your battles much more interesting. And you can customise to the army of your choice (such as Imperial Purple for the legions of Rome or a Woad Blue shade for your ancient Brits!).