Related Clues:

• Kept watch on
• Bugged, with 'on'
• Secretly watched
• Black- -- Susans
• Didn't let out of one's sight
• Leered at
• Was a mole
• Looked at suspiciously
• Excised spud buds
• Observed secretly
• Did secret-agent work
• Kept track of
• Emulated a 29-Down
• Was on a stakeout
• Scoped out