The fist-arm would only work for a sufficiently large dog. Smaller ones, it would not fit. A broom stick instead?
Smaller ones, you just punt.
:)
Seriously though, you can still fit a couple fingers in there.
The effect is the same.
Even the most enraged dog has a strong gag reflex and is extremely averse to strangling on a foreign object.
There’s a psychological component to that, as well.
The dog does not expect its victim to counter attack.
If you don’t freak out and flinch or retreat, it totally screws up their mind.
[how sad is it that we must even speak of such brutal things?]