A common solution for this is lockout-tagout, where you physically lock the breaker open using a lock with your name on it, and nobody can flip it until you come back and take the lock off.
Used on electrical circuits as well as dangerous machines if you need to climb inside a compactor for maintenance or something.
That works too, though IIRC the common procedure in the industry in my country is to use a warning label/shield and hang it on the breaker box during repairs, locking the breaker box itself, then short out the circuit to ground and measure to be sure.
Locks on the breaker itself are more rare (usually for low voltage repairs where the common person might frequent the area)
Used on electrical circuits as well as dangerous machines if you need to climb inside a compactor for maintenance or something.
https://www.osha.gov/Publications/3120.html
http://www.deenergize.com/?target=Universal_Circuit_Breaker_...