Back in the old RPA days, the standard of fencing for different areas of an airport was set out. MOS139 does not contain any fencing requirements, only that you should have one. Nowadays though, I guess it's up to the Airport Operator to interpret the Security Regs, and OTS will rule if they agree with the implementation or not. If you decide to have a security fence, then it would be prudent to meet the Australian Standard (AS1725.1 – 2010) which I assume would help if you were ever in a court room or arguing with OTS.