Who'd act barking? Guard, primarily (8)

I believe the answer is:

watchdog

I'm a little stuck... Click here to teach me more about this clue!

'who'd act barking? guard primarily' is the definition.
I can't tell whether this definition defines the answer.

'who'd act barking? guard primarily' is the wordplay.
'barking?' indicates anagramming the letters (UK slang for mad).
'primarily' indicates taking the first letters.
The initial letter of 'guard' is 'g'.
'whod'+'act'='whodact'
'whodact' is an anagram of 'watchdo'.
'watchdo'+'g'='WATCHDOG'

Can you help me to learn more?

(Other definitions for watchdog that I've seen before include "TV show" , "Kind of guardian, maybe canine" , "Monitoring organisation" , "protector" , "Animal guarding property - guardian against inefficiency or illegality" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.