unfailing

(s) not liable to failure
- a foolproof identification system
- the unfailing sign of an amateur
- an unfailing test
foolproof,
(s) always able to supply more
- an unfailing source of good stories
- a subject of unfailing interest
(s) unceasing
- unfailing loyalty
- unfailing good spirits
- unflagging courtesy
unflagging,

foolproof unflagging

unfailingly