Don't let the disk run out of space. In addition, make sure you don't have to restore or detach the database ever. Make sure you'll never need to drop files.

My personal opinion, if you have to have a copy of the database as it was at a specific point in time, take a backup and either restore it and mark the new DB readonly, or archive the backup. Snapshots are not good for long-term usage or for cases where you absolutely have to have the snapshot. There are too many reasons why you may need to drop them.