Last winter I planned to take pictures of a local nighttime festival and parade with my M10 and 21mm lens. I slipped an external 21mm viewfinder into the accessory shoe and off I went, only to discover that in walking from my car to the event I had lost my viewfinder! Very luckily, I found it the next day in the light. I had not been so lucky in the past. Back when we were using film Leicas, the dropped or lost viewfinder (or other shoe-fit accessory) was an old, sad story. Perhaps today with Live View, people use these viewfinders less, but I don’t.
Through the years, I had spoken at length with such people as Tom Abrahamsson, Don Goldberg, and Stefan Daniel about possible solutions to this, all to no avail. My best idea was to have some sort of swing-up thingy mounted just behind the accessory shoe, to lock the accessory in place. This would entail drilling a mounting hole in the back of the top plate, which thought made all of these fine gents shudder. Suggested to me was simply to put tape in the shoe, so things fit tightly, which is what I had been doing already, and which did not prevent what happened last winter.