Many facilities that I have been involved with, both as an EC, and now as an AHJ have HV services.
The 'service disco' usually is at the point near/where the POCO feeders enter the facility owned equipment. A common setup is a pull section that the POCO cabling terminates in; a PT/CT/etc. then either a "Main" or group of six (6) switches. 'Service' labels must be on the gear. All of this gear is customer owned 7 maintained. Hence, opening the 'main' (or group of six) kills all the power to the facility.
Anything originating from this point outward is considered a feeder, not a service.
Accessability issues re: the locked fence are a local issue to be determined by your AHJ. Breakaway type padlocks are required in some areas; "Knox Boxes" are required in other areas. The fence & gate must be posted with High Voltage signage.
As the HV is distributed thru the facility, and transformed to lower voltages, you have sep. derived systems. Each of these may have primary (HV) and secondary OCP, with the 'main' in the secondary. This by definition is an SDS, not a 'Service'.