I disagree. If the watchdog is external, you have the choice of arranging things so that the watchdog cannot be disabled.
not disabled yes, not toggled no.

All of the derivatives I've used with internal watchdogs (none of which have been selected with the intention of using the internal watchdog) have a single SFR bit that can be cleared at any time to disable the watchdog. I believe this is a pretty common 'feature'.
quoting the Philips P89C51Rx2 and P89C66x datasheets (not necessarily literally)
"once the watchdog is started it can not be disabled"
and "to feed the puppy you must make two consequitve (recommend disabling interrups ) writes of a5 and 5a to sfr xxx."

I consider that mechaninsm much safer than the just toggle a bit that an external watchdog requires.

Erik