I have this plastic chair mat on the carpet below my desk so I can wheel around easy. Only problem is... it shifts in about 3 days time like a foot to the left. I keep on having to move my chair and move it back to where it was. I originally thought "Hey, I could just duct tape the bastard down!" but it seems that it wasn't such a hot idea because the plastic sticky residue crap ends up staying on the carpet when the tape is removed. So here I am... thinking what can I hold it down with, that won't leave residue, and doesn't sit directly on it that is a large object, as that would interfere with my rolling around 
If you are thinking, "WHY the heck is this guy rolling soo much!?" Well, here's a pic that will explain
***PIC***
Eager to hear your suggestions!
If you are thinking, "WHY the heck is this guy rolling soo much!?" Well, here's a pic that will explain
***PIC***
Eager to hear your suggestions!