Run Windows 10 on Mac from custom boot drive? My Mac has specs for Fallout 4, but it won't run with wine like the others. I don't want Windows directly installed on my Mac because it corrupted my hard drive last time, instead I want to install it on a USB 3.0/Thunderbolt drive, where I can hold down a key while booting up my Mac with it plugged in to boot Windows 10. Or something like that. What I have is a Mac with Yosemite and a Windows 10 disk, I need to get an external drive capable of this $30-$50 preferably and suggestions are appreciated.

EDIT: also, I would prefer not to enter many passwords to do this so if possible that would be preferred, if nessesary I can but it would be harder. If it was my computer I wouldn't mind risking corrupting the HD.
rEFInd is able to boot Windows from external drives, as it modifies the Mac's EFI. Here are some instructions on installing it.