I once used to use a strap(for my 300/2.8) but found it more annoying than helpful. I really don't like them!
For resting, the lens hood is always on, so camera is set lens face down on something hard(eg rocks or pavement, or whatever) and then any obstacle is negotiated.

Otherwise a good tripod(carbon fibre) was the better option, clamped properly to the lens foot, front of lens down, over the shoulder legs retracted.
For bushwalking with a large lens, I found best way, and when scrambling over stuff, also use the closed down tripod like a pseudo hiking pole.

A few years later, having met Tony(Tannin) and seeing how he chose to move around, I learned that the pain on the shoulder is minimised with some good padding!
Doh! I knew it, just never thought to do something about it.