[Brian]

I'd recommend using the "Users and Groups" pane of System Preferences to set up a "Repair" account with admin privileges and a different password than you use on your account.

Log out of your account, log into the repair one, and only tell the repair folks the password of the other account. That provides some protection to all your files - email, photos, and so forth - rather than just OmniFocus' files.

Once you get your computer back, you can log into your account and away you go.

For maximum security, enable FileVault in the Security tab of System Prefs as well. That encrypts the data/files in your account on disk while you're not logged into the account.