LogFAQs > #976781686

I would stash it somewhere and never use it till the day I die, hopefully of old age. Possibly looking for a more permanent destruction/burying solution along the way.
Meanwhile, bribing my shinigami w/ apples so he's hopefully cool with an uneventful long term vacation to Earth.

Partly b/c extra judiciously killing people is wrong, but to be honest...mostly for my own survival. If one such book exists, others probably do too, and between rival death note owners and the authorities, the less conspicuous I make myself, the better. Definitely would avoid posting my face to social media and using an alias whenever possible, too.
The mere existence of such a "tool" would terrify me more than anything. I care way more about not-dying than I do about killing "people who deserve it".

EDIT: The one thing I always wondered about the DN is...if you put your own name in there (or had someone else write it in, if you can't "off yourself") and intentionally set the date of your own death so ridiculously far in the future that it'd never occur before you die of natural causes... does that effectively "immunize" you to all death notes? Since your name and time/cause of death is already technically recorded in a death note?
A scheme like that to protect myself and maybe others from less scrupulous DN owners would be my only real interest in "using" it, and I'd still probably be too afraid to test that.