Fighting with target lacking weakness (10)

I believe the answer is:

watertight

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

'fighting with target lacking weakness' is the definition.
I can't judge whether this definition defines the answer.

'fighting with target' is the wordplay.
'fighting' indicates an anagram.
'with'+'target'='withtarget'
'withtarget' anagrammed gives 'WATERTIGHT'.

Can you help me to learn more?

(Other definitions for watertight that I've seen before include "Closely sealed" , "Impermeable - unbreakable" , "seaworthy" , "Without loopholes" , "Unassailable" .)

Want a hint initially instead of a full solution? Install my app