Will Low be adequate for the 50 pound lab? From what I read 40lbs was the “low” there.
If that is not possible then I just move the sensor somewhere that it wont see the dog or maybe disable the motion.
This is difficult to say without testing. The weight limits stated are more a reference to the general height and stature of the animal, and pets climbing on furniture can simulate a much larger object and cause false alarms.
One good option to test over a period of time is to set the Image Sensor as sensor type (23) No Response Type. This will allow you to still set up notifications when it is tripped, and you can gauge how often the dog might set it off and adjust its location to find the best place for it.
Dogs don’t tend to set off pet immune detectors nearly as often as cats, due to the difficulty in keeping cats off of taller objects.
Moving the sensor so that the dog is out of its field of view is the surefire option.