People always laugh when I ask them this!
But honestly, everyone should have a back knobber ....
I keep mine by my desk.
Not only is it useful for muscular tension on the parts of the back you can't reach, it can also fill in the gaps when you are working your spine in a spinal flush (if you know Donna Eden's work you'll know what I'm talking about .... if not watch out for my next blog) or when trying to reach a specific acupressure point on the back.
So if you don't have a great physio/masseuse close to hand, explore the possibilities of a 'back knobber'.