I know a 150 feet standard ethernet cable ( orange ) standing 3 years outside. Its in western europe in a most shadow situation.
Now the cable has a white facing and is a bit nonelastic but work.

I think it depends your climate.

Gernot

p.s. don' t dig the cable.

you should consider galvanic isolation, if both ends got their own earthing system then you should use an optical not electrical system.