VPN Security or secure instant linux

Howto increase VPN security, when you only need remote desktop or remote login sessions? 

When your OS at office is Win2008,  VPN clients on bootable write protected memory sticks/ CDs/ DVDs with a special prepared linux OS can enhance security. (You can easy clone or customize a live cd and change the certificate / password all 2 months)  You might even prepare a live cd for android or boot a special image from sdcard, but remember, that an image on sdcard isn't write protected.