Christina,
The lens is safely stored inside a closed, soft case that provides plenty of padding (as are my polarizers and speedlight). The case has a flap on the back extending the entire length of the case. That flap is inserted between the wide strap on the bag and the bag itself. The flap is then attached to its case with snaps built into the bottom of the strap and with velcro built into the flap and the case. Any secure third-party accessory that has a flap that will fit into the strap on the bag will work but I have always bought
Tamrac cases because they are designed as part of the system.
I've walked miles with that darned lens over all kinds of terrain and have never felt anything other than its weight. In the future, I'm gonna be more discriminating about how far I carry it just because of the added weight, not out of any concern for safety. Otherwise, I'll ask my wife to carry it.