How to disable MacBook Pro power during sleep?

[Xscapes]

I have my external HD connect to the usb port, it always powered on even in sleep mode. I want to know if theres anyway to disable the power when the computer is sleeping.

 

[Gilj]

Im not sure if it's unmount only or disable the power too, but I use this :
http://www.macworld.com/article/1163496/jettison_automatically_unmounts_volumes_when_your_mac_sleeps.html.