Heres a rough draft of what you need
Theres some more details, depending on your specific pulse width and the amount of lightning / surge protection you need. The opto-22 modules could be used instead, they have pretty good protection built in.
There are mcuh cheaper ways to do this using just a few resistors, but I went this way for emphasis on rugged and long-term reliable in what could be a nasty electrical environment.
You'd save about $50 to $150 going the cheaper way. Gotta be sure all counters share one common lead that can be grounded and tied to Arduino ground, then use resistors, capacitor and diodes to DIO pins.