I have a zspray. If I needed to spray a fence line I'd just use the outside nozzle. You'd need to go down both sides I would think depending on how wide a band you need. Using 1 nozzle would get you 1-2 foot band on each side.
Theoretically you would be able to spray you calibrated rate. If you are set at 1/3 gallon per 1000 then you should be able to do one side of fence at 1500 ft per gallon. I'd figure less since you say it's bumpy.