Its done all the time in corporate environments, although fibre is now the way to go.
For home users, the key is using conduit, as you've said you will. That's because the ground shifts over time and even a person walking over buried wire might have an effect. The conduit has to be completely water-tight, and there must be no ethernet cable joints, couplers, or other connections within the conduit. Both ends of the conduit must be above ground (hopefully a foot or two).
You can even purchase a shielded ($$$) run of Cat5e or Cat6, not necessarily for any EMF effects but just for more solidity to the cable.