I use thick Velcro, specifically something like this http://www.velcro.com/Products/Ties-and-Straps/Ties/One-Wrap-Tie-Rolls.aspx
I have a piece between the units, and a wrap around them. It's thick enough to basically be feet; keeps the O2 off the table and the ODAC from sliding on the O2. It can also be taken apart and the units separated without leaving any trace since it isn't adhesive.
You can see it in the background here (with a velcro-wrapped cable on top so I can carry it around):
Edited by trueserve - 1/18/13 at 9:54pm