Possible Clues:

• Like some academic positions
• Number terribly rude unfortunately unable to be sacked?
• Nurse keeping clean but without pressure, having secure job
• Like some university professors
• Unlikely to be removed from office, having settled rent due
• Not easily let go
• Secure in one's teaching job
• With time guaranteed, though last of students drops out?
• Plastic denture kept for an agreed time
• Holding a permanent post