I have never been assaulted at work or been seriously concerned about a patient hurting me. I've had my fair share of old grannies with alzheimer's being combatant, but I don't consider that assault any more than I consider my dog assaulting me as he tries to get out of taking a bath.
I use common sense to protect myself, but I'm not sure that's enough. If I still worked the road a lot, I would
absolutely take a defensive training course suited towards EMS. I know one of our users, DT4EMS has a
website where he sells an instructional video, and I've been meaning to buy one for a long time now.
With regular partners I've also had code words that I could yell out and the driver would light it up and slam on the brakes. That may give me an edge if I was fighting in the back. We could always radio for PD, though I think a 5-10 minute response would be normal (We'd radio dispatch, dispatch would have to contact PD, they would be dispatched.. you get the picture).
I think it's absolutely essential, if EMS is your career, to take a defensive tactics course. I simply don't work enough, and 99% of my calls are dialysis / BLS calls.