jeffez:
Thanks, so I would want more current running from the Arduino on the left given the long distance to ground?
No, the gain of the optocoupler is (usually) less than one, likely about 50%, so you need to feed more current into it than it can switch with the output transistor, thus the lesser resistance. It has no relationship to the distance.
Your diagram is however wrong - the optocoupler should be on the receiving side with the cable feeding the LED. The cable resistance will merely be part of, but almost certainly much less than the current limiting resistor for the LED.
jeffez:
Would a capacitor be worth using the help smooth out potential noise from the long distance?
Almost certainly not. Unless your signal is very slow, perhaps 10 baud.