Track large lizard (7)
I believe the answer is:
monitor
I believe this clue is a double definition.
'track' is the first definition.
(to track or keep an eye on)
'large lizard' is the second definition.
(monitor is a type of lizard)
(Other definitions for monitor that I've seen before include "Check on - large lizard" , "in-class help" , "Keep a watching brief" , "Supervisor - lizard" , "Sort of lizard" .)