Lockable Pin Back
All my enamel pins come with a metal butterfly back, but to make doubly sure your pin is secure you can use one of these lockable pin backs. This listing is for one lockable pin back.
The metal butterfly backs are fine for occasional wear on a lapel or jumper, but if you want to place your pin on something that gets more wear and tear and bumped around, like a bag or permanently fixed to a jacket I'd recommend using a lockable back.
To use one of these backs place the pin spike through your fabric and push the lockable pin back onto the spike at the back, if it is a bit stiff pull the back circle of the lockable pin back out (it's sort of on a spring) push it over the spike and let go of the springed back circle. The back is now locked in place. To take it off simply pull the back circle bit out again and pull it off the spike.