I've got an air 'froghorn' at the mo, but getting stuck in fog for a while could make that run out of air, and then I'd be stuck.
Was looking at getting a trumpet style horn for the a-frame, but when sounding it, I wasn't sure whether I'd have any ear drums left afterwards - not heard one when stood a couple of metres infront before
One of my mates down here has like a car horn on his a-frame, but after a few weeks, it changed tone, and now sounds like a noddy car horn - it's also got a lot quieter with water ingress..... I guess this is mostly to do with salt as opposed to water though.
-Alex