Keeping watch, running aground (2,5)
I believe the answer is:
on guard
'keeping watch' is the definition.
(I've seen this before)
'running aground' is the wordplay.
'running' indicates an anagram (the letters run around to different places).
'aground' is an anagram of 'ON GUARD'.
(Other definitions for on guard that I've seen before include "Watchful" , "Alert like sentry" , "Wary" , "Keeping watch" , "Alert, vigilant" .)