Annoying problem, especially when the nut falls off and the little bolt comes out and the dog is moving around. I stocked up on those little 8mm nuts just for this reason.
I don't know it this makes a difference or not but using a wrench may give give you more torque than say a nut driver which is my tool of choice because the carbs have the same size nut. The last time I had to do this on a 66 and a 361. I used a wrench and no problem since, that was months ago.
Like Butch said,routine and boring maintenace will take care of the problem if a guy can remeber to do it.
Never gave it much thought but the problem may not be the nut itself but too much vibration coming from the saw from worn rubber stiff shocks, jerky cutting chain ect. ect. I dunno know.