I thought you can but when I tried it, there is no sec 179 option in the Rental Properties section. I'm going to look into this today and reply back.
I suggest if you built a new Ag fence or did an expensive major rebuild to the fence to depreciate it, otherwise write it off as an expense in Repairs and Maintenance. Ag fencing uses a seven year recovery period, 150DB as described in the page snip below;
