Mirror for Exchange DR

I work in an organization committed to ensuring DR for all systems. This has been accomplished very professionally for every other platform, ensuring mirrored copies of data across a Frame Relay network to remote sites both within New Zealand and, for one application, to Australia as well.
Except for Exchange. This is not mirrored as it does not allow itself to be. Instead there are backup tapes sent each day to the distant office, incurring inevitable risk for accidental erasure or damage to the tape, and consequent loss of data.
What tools and techniques are available to ensure the remote Exchange Server is able to maintain an up-to-date database and also to eb dynamically available if the local serve should fail?