Maybe rates go to 6, 7, 8% and you're underwater, but where we're at today feels like it's closer to the long term mean.
I think the issue though, at least from my pov, is rates at 8% would probably be because of another breakout in inflation and so when the bond price has fallen 30%-40% you either take the real capital loss to get higher rates, or ride it out and take the slow burn corrosion of inflation eating away at the face value. I guess it's just my own mindset toward cash is that it's not something that should ever keep me up at night.
I have to be honest, I just keep my cash in a couple of Macquarie accounts and an ANZ account which is pretty lazy. I guess you could go down the FRN path too, but federal government guarantees bank accounts to $250k/account which if you were chasing yield seems tough to beat given some of the rates I see from a quick look around and seems to make it the most compelling.