Dog behind fences runs (5)
I believe the answer is:
trail
'dog' is the definition.
(both can mean to follow)
'behind fences runs' is the wordplay.
'behind' becomes 'tail' (synonyms).
'fences' indicates putting letters inside (inserted letters are fenced off).
'runs' becomes 'r' (cricket abbreviation).
'tail' going around 'r' is 'TRAIL'.
(Other definitions for trail that I've seen before include "Get behind" , "Need to catch up with" , "Dog - track" , "Straggle" , "Forest path" .)