How can I keep my glasses from slipping out of my pocket?

I carry my reading glasses in the breast pocket of my shirt. Whenever I bend over, the glasses slip out and hit the floor, carpet, road, concrete or whatever. I have gotten reasonably good at putting my hand on my pocket to prevent the glasses from slipping out, but sometimes I need both hands for whatever I am doing.

I know I could put the glasses in some kind of case, but I am already enough of a nerd without a bulky case in my shirt pocket.

I have a half baked idea to put magnets on the ear arm part of the glasses to clamp them to the shirt pocket (one arm outside, one inside), but there must be a better way.

Any ideas how I can keep my glasses from slipping out of my pocket?