[Az-Geocaching] Eternal Cache Container

[Lasivian]

ok, I need ideas for a cache container for a cache that might be 
found once a year, or once every 10 years even

requirements:

Rustproof
Airtight
Photo-resistant (Sun won't rot it)
Internal size at least 1728 cubic inches (ie, 12"x12"x12", but the 
shape doesn't matter)
Must be resitant to stress/impacts (ie. if it breaks when I hit it with 
a hammer, or I can bend it in half it's no good)
Can't have keys/lock (tho a combination lock might not be bad)

my general target is a minimum of 100 years, it will be hidden in 
Arizona

so far the only thing I can think of is a custom-built stainless 
"Container", or maybe a Sentry-type firesafe

thanks