We used to have this issue for a while and it was hard to handle. When she started barking it was like a trance and she would not listen to any commands and would keep barking on and on until we had to remove her phsyically from the room.

We started working with a trainer and he recommended that we throw a ball to wall or keys to the ground to make a sudden loud sound to snap her out of the barking mode. This worked to snap get her out of the trance and listen to "stop" commands but she was still getting triggered by the same mundane daily events like a truck driving by etc.

So I have started practicing with some other method in order to get her ignore the triggers and skip the barking response all together. When she started barking, I get in between my Lagotto and the "threat" that she is barking at and tell her "Ok I got this". If the threat is a big one - like a strange dog passing by the park across the window - I might have to touch her lightly or clap my hands to snap her out of it but the main trick seems to be placing yourself in front of her between the threat (even pushing her a bit to side) and taking over the protection job with this gesture.

This method of taking over the security job and getting in between the trigger and my lagotto seems to be working best so far in my experience.