keep guard (on)
guard
keep watch (on)
police
walk the beat (of)
pound the beat (of)
make the rounds (of)
walk along/around
range (over)
perform sentry duty (on)
picket
stand guard (over)
keep a vigil (on)
keep a lookout (over)
cover
monitor
defend
safeguard
cruise
pound
prowl
rove
roam
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