Park officer (6)
I believe the answer is:
ranger
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">park officer</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for ranger that I've seen before include "Forest or park keeper" , "park-keeper" , "Park warden" , "Keeper of national park or Texas policeman" , "National park officer" .)