Decision provided enclosure at last, confining 500 animals (8)
I believe the answer is:
wildlife
'animals' is the definition.
(I've seen this before)
'decision provided enclosure at last confining 500' is the wordplay.
I cannot really understand how this works, but
'provided' could be 'if' (eg 'provided it's sunny' means 'if it's sunny') and 'if' is located in the answer.
'500' could be 'd' (Roman numeral for 500) and 'd' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for wildlife that I've seen before include "Undomesticated fauna and flora" , "All undomesticated creatures" , "Native fauna" , "All untamed creatures" , "Creatures in their natural habitat" .)