It is not necessary to obtain an ILP to build a fence. However, you are required to abide by regulations stated in the Unified Zoning Ordinance.
Fences may be built on the property line. The county GIS map will give you a good indication of the location of your property lines. A survey should be done to get a precise location of property lines.
Reference: Article II of the Unified Zoning Ordinance section 2.02.