I agree with fenrir, no need to do it for a single player oriented game. I'd only consider it if scumming interferes with someone else's fun.
I put a little bit of thought into this. I was thinking I might allow the player to save online stats. In which case a scum save can interfere with anothers' fun.
If the player wants to use online stats I would host an internet server. The server would generate a per character SSL key. The character on death has the option to upload the character stamped with this key.
Several things would be tracked for the online save option:
1. A saved file itself would contain a time stamp of the last save file modified time. If the modified time is mysteriously changed after the time stamp, it was scummed or edited externally. Encryption here also would help ensure the data confidentiality (from the user).
2. The current state of the character (dead, loaded, playing, saved, hacked) is saved. If the character state is in playing state, and the game is loaded, it will flag a hacked state. Computers being unstable (including the app), I might allow a grace load for a character, which could be reset after a certain period of time ( maybe 1 hour).
3. To prevent memory hacking, you can generate a CRC of the core statistics of the player. This value is checked after every change and then a new CRC is generated.
4. While playing the save system would stream data in the game to the save character file every 5-10 seconds including the above mentioned game state.
On death, the character data when received by the server is checked to make sure it wasn't a hack. Things like time span of character life, HP, AC, items, kills, or whatever else I want checked. For example, a 1 hour life span of a level 50 character = fail.
Hrmm. Maybe this would be overkill too. Just a few thoughts off the top of my head.