I didn't mean to imply that an OPTIMA can't fail...anything manmade has that ability, but an OPTIMA probably won't fail due to the typical weaknesses of a lead acid type battery.
Since an OPTIMA is usually smaller than an oem type battery, you may have to alter your oem type hold down/tray. The OPTIMA (from COSTCO) typically comes with two red plastic adapters that may allow you to use you oem hold down/tray without much modification.
You can also do that as others suggested or if you want to spend the money, there are several billet type brackets that are OPTIMA specific.
If you intend to trunk mount your OPTIMA, then a battery box will be a good idea. I used a generic black plastic battery box for my OPTIMA, but RB'S OBSOLETE has a really nice compact ABS battery box now. http://www.rbsauto.com/