I highly recommend a velcro strap to keep it on the frame. FIWI, I retired my frame pump because of a number of annoying things:
- rattled too much on the lousy pavement around here
- the little plug that keeps the the pump hole closed would never stay in place, rubbing my leg
- even with the velcro it would fall off sometimes (it would stay on, but flop around, dangerous on a big descent)