no one has ever bricked using ModMii, and there is no safer method (although there are probably other guides that are equally safe). One of the first steps of your modmii guide is to make a nand backup, that backup can be used to recover from any normal type of brick, although u may need to send it to someone like DeadlyFoez to repair it unless you have an older model wii, in which case recovery with bootmii installed to boot2 is very easy.
Assuming you're following a ModMii Wizard guide, the only risk of bricking is if you lose power during the installation of priiloader, your system menu IOS WAD, or a system menu WAD (which is often not even required to be installed). Basically, if u lose power at the exact wrong moment u can brick, but the total time where power failure may lead to brick is about 5-30 seconds (about 30 seconds only if a system menu WAD is being installed, which is only a part of your guide if you're starting on a system menu version of 4.0 or less). Even if this happens, you can recover your wii using your nand backup and some infectus modchip knowhow. And if you're wii is an older model, you can recover even if you don't have a nand backup or infectus.
The only way to protect against a semi-brick due to power loss is to get yourself a surge protector with battery backup. But as I said, even newer model wii's can be recovered as long as you have a nand backup.