Rigid rotation of two surfaces

Hi all
Is there a way to perform a rigid rotation of multiple surfaces?
For example, imagine two simple surfaces at right angle, with and edge in common.
I would like to tell Rhino, that if I rotate or move just one surface, then the the relative position of the second surface, with respect the first one, stays the same.

I know I can join them together, but I would like to be able to assign a constraint without joining.

Thank
Pier

Have you tried group or block?

Thank you for the quick reply, and apologies form late response.
That will do the job.