DMT Diafold Magna-Guide Sharpening System for swapsies.
This is the easiest and fastest system I've used for putting a perfect edge onto your folders in seconds.
There are different settings, to enable shallower or steeper angles. Lightweight and portable, will last a looong time.
The System costs £45.95 from Heinnie: http://www.heinnie.com/product.asp?P_ID=4796
I have the double sided Blue/Red Combination DMT Diafold. [The most popular combination.]
BLUE=Diamond - Coarse
Quickly sharpen a neglected edge, 325 mesh, 45 micron.
RED=Diamond - Fine
Put a keen edge on a maintained tool, 600 mesh, 25 micron.
The system is like new, as I only used it a handful of times for my spyderco UKPK.
I am after a good quality Largish Tarp.