saw the message about shielding of traces and I'd add to the "pot". My
experience with guard traces has not been fruitful, except when I used them
to protect the inputs of operational amplifiers. In this situation you
actually drive the guard trace.
On higher speed circuits, I've had much more success keeping to sound
transmission line concepts: slower signals routed as micro-strip on outside
layers, faster signals as strip lines on inside layers. Distance and
orentation are the best ways to prevent line interaction. On larger layouts,
there may not be room for all the extra traces...
In reality, if your customer asks for it and you cannot reason why, give them
what they ask for. You may learn if it works, you look smarter if it doesn't.
Good luck, and report back to the list what you learn.
Derek N. Walton.
Owner L F Research EMC Design and Test Facility