Mounting den peguanum on rock

[Chriss]

I was advised by my local FB newb group to repot my den peguanum as the moss is yellow and dying. I have a rock I'd like to use as a mount, and I need advice on whether it's a good choice, and if so how to prepare it. It's been a bookend on a shelf for years.

I thought to use a little spagnum and then secure it with fishing line.

Any advice or hints much appreciated.