Good gosh, an aluminum tube?
How about a loosely rolled newspaper? It isn’t about the pain, it is about the gesture, the physical display of displeasure.
The loosely rolled paper allows for noise and a harmless (whooshy) whack, and even a harmless expression/release of the owner’s anger, yet covers all the bases of a firm expression of displeasure with a dog doing something intolerable, and for which other methods haven’t prevented him from doing.
IT was light - it would have bent if we had of struck him hard with it!