mounting a safe

I've seen a few under the steps which means that is probably the first place a real thief will look. I would think the floor is the only really "secure" spot since you could totally enclose the safe and make it harder to rip out. They could get it out with a bit of work, but it will make noise and that may be a deterrent.

The other side of the coin is that the thieves see a safe and instantly think "Valuables worth stealing" and may make the effort necessary to get to it. Definitely needs to be out of sight.