Just picked up an SB Tactical SOB-47 brace.  It twists pretty easy, much easier than the default SB Tactical old style brace.  Any kind of non-permanent solutions to keep it from rotating?

Electrical tape around tube fixed all my loose braces.

Sounds like a good idea.

Frontrunner so far.  

I had an older SB-47 brace which is shorter than my SOB and started to rotate, and I wanted to bring it back a few inches so I used some 3M 77 spray adhesive, it's slippery when first sprayed so it's easy to position the brace then when it dries it's rock solid. But it'll never move again. Another option that's reversible is to pin the tube, either a small screw or a nail.

I also have an SOB on an AK pistol and another SOB on an AR pistol. So far they have not rotated yet. But they probably will. SB really needs to just pin these from the factory, the friction fit isn't a good long term setup.

Agreed, they really should pin them.  The original brace doesn't rotate at all, but it's heavy and fugly.

Hairspray.

Double sided tape from wal mart