How can I make Asus M4A78LT to boot from USB-flash only and not to change priority

[ev-gen]

Hi to everybody!
First of all I'm sorry for my English.

I have a PC with motherboard Asus M4A78LT, 2 HDD without boot partition and USB-flash drive with boot. Everything is OK and PC booting from USB-flash.

But there is a problem. If I remove my USB-flash and then reboot my PC - BIOS changes boot priority for HDD drives as a highest. And then if I insert the USB-flash its priority becames a lowest. And PC doesn't boot from it. And I must to edit BIOS settings again and again to boot from USB-flash.


Help me please make motherboard to boot only from USB in any conditions and not to change a priority of bootable media.