Originally Posted by Bandera

Revracer.

Good on you, glad you are enjoying it.

Before venturing out again remove your derail, shorten the chain (or install a fresh one) & re-install the wheel.
Please read Sheldon Brown on the conversion process & heed his warning:

"You CanNOT use any sort of pulley type chain tensioner on a fixed gear bike!"

http://sheldonbrown.com/fixed-conversion.html

-Bandera