$6 cosmetic battery tie-down fasteners.
 

I swapped-out the huge OE Panasonic battery last year for a sealed Optima battery. The Optima was a little shorter and I've been driving around with 2" of exposed all-thread. So today I finally remembered to cut down those little all-thread tie-downs. Hit the hardware store after work and bought a pair of black nylon wing-nuts with 6mm threaded brass inserts and a pair of 1/8" thick white nylon washers. I think it looks pretty clean. Total cost was $6.00

http://i.imgur.com/7XiUifI.jpg

http://i.imgur.com/5RXAxHx.jpg

This is completely off-topic, but is it safe if I don't have the red positive cover on my battery?

That cover is cheap insurance. It is there for the remote chance of you dropping a conductor (spanner,screwdriver, not the person who leads an orchestra) on the positive terminal and earth while the negative terminal is still connected to the earth lead. If that happens..... no, you are not going to let that happen.